(INCOMPLETE: ES6 Module conversion and linting)

- Breaking change: Require `new` with `EmbeddedSVGEdit` (allows us to use `class` internally)
- Breaking change: If `svgcanvas.setUiStrings` must now be called if not using editor in order
    to get strings (for sake of i18n) (and if using path.js alone, must also have its `setUiStrings` called)
- Breaking change (ext-overview-window): Avoid global `overviewWindowGlobals`
- Breaking change (ext-imagelib): Change to object-based encoding for namespacing of
    messages (though keep stringifying/parsing ourselves until we remove IE9 support)
- Breaking change: Rename `jquery.js` to `jquery.min.js`
- Breaking change: Remove `scoped` attribute from `style`; it is now deprecated and
    obsolete; also move to head (after other stylesheets)
- Enhancement: Make SpinButton plugin independent of SVGEdit via
    generic state object for tool_scale
- Enhancement: Remove now unused Python l10n scripts (#238)
- Enhancement: ES6 Modules (including jQuery plugins but not jQuery)
- Enhancement: Further JSDoc (incomplete)
- Enhancement (Optimization): Compress images using imageoptim (and add
    npm script) (per #215)
- Fix: i18nize path.js strings and canvas notifications
- Fix: Attempt i18n for ext-markers
- Refactoring (ext-storage): Move locale info to own file imported by the extension (toward modularity; still should be split into separate files by language and *dynamically* imported, but we'll wait for better `import` support to refactor this)
- Refactoring: For imagelib, add local jQuery copy (using old 1.4.4 as had
    been using from server)
- Refactoring: For MathJax, add local copy (using old 2.3 as had been using from
    server); server had not been working
- Refactoring: Remove `use strict` (implicit in modules)
- Refactoring: Remove trailing whitespace, fix some code within comments
- Refactoring: Expect `jQuery` global rather than `$` for better modularity
    (also to adapt line later once available via `import`)
- Refactoring: Prefer `const` (and then `let`)
- Refactoring: Add block scope keywords closer to first block in which they appear
- Refactoring: Use ES6 `class`
- Refactoring `$.isArray` -> `Array.isArray` and avoid some other jQuery core methods
    with simple VanillaJS replacements
- Refactoring: Use abbreviated object property syntax
- Refactoring: Object destructuring
- Refactoring: Remove `uiStrings` contents in svg-editor.js (obtains from locale)
- Refactoring: Add favicon to embedded API file
- Refactoring: Use arrow functions for brief functions (incomplete)
- Refactoring: Use `Array.prototype.includes`/`String.prototype.includes`;
    `String.prototype.startsWith`, `String.prototype.trim`
- Refactoring: Remove now unnecessary svgutils do/while resetting of variables
- Refactoring: Use shorthand methods for object literals (avoid ": function")
- Refactoring: Avoid quoting object property keys where unnecessary
- Refactoring: Just do truthy/falsey check for lengths in place of comparison to 0
- Refactoring (Testing): Avoid jQuery usage within most test files (defer script,
    also in preparation for future switch to ES6 modules for tests)
- Refactoring: Make jpicker variable declaration indent bearable
- Refactoring (Linting): Finish svgcanvas.js
- Docs: Mention in comment no longer an entry file as before
- Docs: Migrate old config, extensions, and FAQ docs
- Licensing: Indicate MIT is license type of rgbcolor; rename/add license file name for
    jgraduate and screencast to reflect type (Apache 2.0); rename file to reflect it
    contains license information (of type MIT) for Raphael icons

editor/extensions/ext-closepath.js

@@ -1,5 +1,4 @@
-/* eslint-disable no-var */
-/* globals svgEditor, $ */
+/* globals jQuery, svgEditor */
 /*
  * ext-closepath.js
  *
@@ -8,41 +7,42 @@
  * Copyright(c) 2010 Jeff Schiller
  *
  */
+// import './pathseg.js';
 
 // This extension adds a simple button to the contextual panel for paths
 // The button toggles whether the path is open or closed
 svgEditor.addExtension('ClosePath', function () {
-  'use strict';
-  var selElems,
-    updateButton = function (path) {
-      var seglist = path.pathSegList,
-        closed = seglist.getItem(seglist.numberOfItems - 1).pathSegType === 1,
-        showbutton = closed ? '#tool_openpath' : '#tool_closepath',
-        hidebutton = closed ? '#tool_closepath' : '#tool_openpath';
-      $(hidebutton).hide();
-      $(showbutton).show();
-    },
-    showPanel = function (on) {
-      $('#closepath_panel').toggle(on);
-      if (on) {
-        var path = selElems[0];
-        if (path) { updateButton(path); }
+  const $ = jQuery;
+  let selElems;
+  const updateButton = function (path) {
+    const seglist = path.pathSegList,
+      closed = seglist.getItem(seglist.numberOfItems - 1).pathSegType === 1,
+      showbutton = closed ? '#tool_openpath' : '#tool_closepath',
+      hidebutton = closed ? '#tool_closepath' : '#tool_openpath';
+    $(hidebutton).hide();
+    $(showbutton).show();
+  };
+  const showPanel = function (on) {
+    $('#closepath_panel').toggle(on);
+    if (on) {
+      const path = selElems[0];
+      if (path) { updateButton(path); }
+    }
+  };
+  const toggleClosed = function () {
+    const path = selElems[0];
+    if (path) {
+      const seglist = path.pathSegList,
+        last = seglist.numberOfItems - 1;
+      // is closed
+      if (seglist.getItem(last).pathSegType === 1) {
+        seglist.removeItem(last);
+      } else {
+        seglist.appendItem(path.createSVGPathSegClosePath());
       }
-    },
-    toggleClosed = function () {
-      var path = selElems[0];
-      if (path) {
-        var seglist = path.pathSegList,
-          last = seglist.numberOfItems - 1;
-        // is closed
-        if (seglist.getItem(last).pathSegType === 1) {
-          seglist.removeItem(last);
-        } else {
-          seglist.appendItem(path.createSVGPathSegClosePath());
-        }
-        updateButton(path);
-      }
-    };
+      updateButton(path);
+    }
+  };
 
   return {
     name: 'ClosePath',
@@ -53,7 +53,7 @@ svgEditor.addExtension('ClosePath', function () {
       panel: 'closepath_panel',
       title: 'Open path',
       events: {
-        click: function () {
+        click () {
           toggleClosed();
         }
       }
@@ -64,19 +64,19 @@ svgEditor.addExtension('ClosePath', function () {
       panel: 'closepath_panel',
       title: 'Close path',
       events: {
-        click: function () {
+        click () {
           toggleClosed();
         }
       }
     }],
-    callback: function () {
+    callback () {
       $('#closepath_panel').hide();
     },
-    selectedChanged: function (opts) {
+    selectedChanged (opts) {
       selElems = opts.elems;
-      var i = selElems.length;
+      let i = selElems.length;
       while (i--) {
-        var elem = selElems[i];
+        const elem = selElems[i];
         if (elem && elem.tagName === 'path') {
           if (opts.selectedElement && !opts.multiselected) {
             showPanel(true);