move files to adequate folders and fix imports

src/common/namespaces.js

@@ -0,0 +1,33 @@
+/**
+ * Namespaces or tools therefor.
+ * @module namespaces
+ * @license MIT
+*/
+
+/**
+* Common namepaces constants in alpha order.
+* @enum {string}
+* @type {PlainObject}
+* @memberof module:namespaces
+*/
+export const NS = {
+  HTML: 'http://www.w3.org/1999/xhtml',
+  MATH: 'http://www.w3.org/1998/Math/MathML',
+  SE: 'http://svg-edit.googlecode.com',
+  SVG: 'http://www.w3.org/2000/svg',
+  XLINK: 'http://www.w3.org/1999/xlink',
+  XML: 'http://www.w3.org/XML/1998/namespace',
+  XMLNS: 'http://www.w3.org/2000/xmlns/' // see http://www.w3.org/TR/REC-xml-names/#xmlReserved
+};
+
+/**
+* @function module:namespaces.getReverseNS
+* @returns {string} The NS with key values switched and lowercase
+*/
+export const getReverseNS = function () {
+  const reverseNS = {};
+  Object.entries(NS).forEach(([name, URI]) => {
+    reverseNS[URI] = name.toLowerCase();
+  });
+  return reverseNS;
+};