(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-helloworld.js

@@ -1,5 +1,4 @@
-/* eslint-disable no-var */
-/* globals svgEditor, svgCanvas, $ */
+/* globals jQuery, svgEditor, svgCanvas */
 /*
  * ext-helloworld.js
  *
@@ -16,8 +15,7 @@
 */
 
 svgEditor.addExtension('Hello World', function () {
-  'use strict';
-
+  const $ = jQuery;
   return {
     name: 'Hello World',
     // For more notes on how to make an icon file, see the source of
@@ -38,7 +36,7 @@ svgEditor.addExtension('Hello World', function () {
 
       // Events
       events: {
-        'click': function () {
+        click () {
           // The action taken when the button is clicked on.
           // For "mode" buttons, any other button will
           // automatically be de-pressed.
@@ -48,7 +46,7 @@ svgEditor.addExtension('Hello World', function () {
     }],
     // This is triggered when the main mouse button is pressed down
     // on the editor canvas (not the tool panels)
-    mouseDown: function () {
+    mouseDown () {
       // Check the mode on mousedown
       if (svgCanvas.getMode() === 'hello_world') {
         // The returned object must include "started" with
@@ -59,16 +57,16 @@ svgEditor.addExtension('Hello World', function () {
 
     // This is triggered from anywhere, but "started" must have been set
     // to true (see above). Note that "opts" is an object with event info
-    mouseUp: function (opts) {
+    mouseUp (opts) {
       // Check the mode on mouseup
       if (svgCanvas.getMode() === 'hello_world') {
-        var zoom = svgCanvas.getZoom();
+        const zoom = svgCanvas.getZoom();
 
         // Get the actual coordinate by dividing by the zoom value
-        var x = opts.mouse_x / zoom;
-        var y = opts.mouse_y / zoom;
+        const x = opts.mouse_x / zoom;
+        const y = opts.mouse_y / zoom;
 
-        var text = 'Hello World!\n\nYou clicked here: ' +
+        const text = 'Hello World!\n\nYou clicked here: ' +
           x + ', ' + y;
 
         // Show the text using the custom alert function