Add static js and css for markdownit and plugins

- MFR uses the same markdown-it.js and its plugins
  as OSF for rendering MD. However, due to lack of
  package managing and Babel, all full scripts are
  manually eslinted and babeled if necessary. .min
  scripts are kept intact.

Author: cslzchen

mfr/extensions/md/static/css/default.css

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+@charset "utf-8";
+
+.mfrViewer {
+    font-family: 'Open Sans';
+    padding: 1em;
+    background: #fefefe;
+    height: auto;
+    word-wrap: break-word;
+}

mfr/extensions/md/static/css/highlightjs-default.css

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+/**
+ * Original highlight.js style (c) Ivan Sagalaev <maniac@softwaremaniacs.org>
+ *
+ * https://github.com/isagalaev/highlight.js/blob/9.12.0/src/styles/default.css
+ */
+
+.hljs {
+    display: block;
+    overflow-x: auto;
+    padding: 0.5em;
+    background: #F0F0F0;
+}
+
+
+/* Base color: saturation 0; */
+
+.hljs,
+.hljs-subst {
+    color: #444;
+}
+
+.hljs-comment {
+    color: #888888;
+}
+
+.hljs-keyword,
+.hljs-attribute,
+.hljs-selector-tag,
+.hljs-meta-keyword,
+.hljs-doctag,
+.hljs-name {
+    font-weight: bold;
+}
+
+
+/* User color: hue: 0 */
+
+.hljs-type,
+.hljs-string,
+.hljs-number,
+.hljs-selector-id,
+.hljs-selector-class,
+.hljs-quote,
+.hljs-template-tag,
+.hljs-deletion {
+    color: #880000;
+}
+
+.hljs-title,
+.hljs-section {
+    color: #880000;
+    font-weight: bold;
+}
+
+.hljs-regexp,
+.hljs-symbol,
+.hljs-variable,
+.hljs-template-variable,
+.hljs-link,
+.hljs-selector-attr,
+.hljs-selector-pseudo {
+    color: #BC6060;
+}
+
+
+/* Language color: hue: 90; */
+
+.hljs-literal {
+    color: #78A960;
+}
+
+.hljs-built_in,
+.hljs-bullet,
+.hljs-code,
+.hljs-addition {
+    color: #397300;
+}
+
+
+/* Meta color: hue: 200 */
+
+.hljs-meta {
+    color: #1f7199;
+}
+
+.hljs-meta-string {
+    color: #4d99bf;
+}
+
+
+/* Misc effects */
+
+.hljs-emphasis {
+    font-style: italic;
+}
+
+.hljs-strong {
+    font-weight: bold;
+}

mfr/extensions/md/static/js/markdown-it-highlightjs.js

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+/**
+ * Preset to use highlight.js with markdown-it.
+ *
+ * Origin: https://github.com/valeriangalliat/markdown-it-highlightjs/tree/v3.0.0/index.js
+ *  The above link gives a 404. Here is a forked copy and Babel-converted ES5 version:
+ *  (ES6) https://github.com/cslzchen/markdown-it-highlightjs/blob/release/3.0.0/index.js
+ *  (ES5) https://github.com/cslzchen/markdown-it-highlightjs/blob/release/3.0.0/index.es5.js
+ *
+ * Version: https://github.com/valeriangalliat/markdown-it-highlightjs/releases/tag/v3.0.0
+ */
+
+(function (root, factory) {
+    if (typeof exports === "object") {
+        module.exports = factory();
+    } else {
+        root.markdownitHightlightjs = factory();
+    }
+})(this, function () {
+
+    "use strict";
+
+    var maybe = function maybe(f) {
+        try {
+            return f();
+        } catch (e) {
+            return false;
+        }
+    };
+
+    // Highlight with given language.
+    var highlight = function highlight(code, lang) {
+        return maybe(function () {
+            return hljs.highlight(lang, code, true).value;
+        }) || "";
+    };
+
+    // Highlight with given language or automatically.
+    var highlightAuto = function highlightAuto(code, lang) {
+        return lang ? highlight(code, lang) : maybe(function () {
+            return hljs.highlightAuto(code).value;
+        }) || "";
+    };
+
+    // Wrap a render function to add `hljs` class to code blocks.
+    var wrap = function wrap(render) {
+        return function () {
+            for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
+                args[_key] = arguments[_key];
+            }
+
+            return render.apply(this, args).replace("<code class=\"", "<code class=\"hljs ").replace("<code>", "<code class=\"hljs\">");
+        };
+    };
+
+    var defaults = {
+        auto: true,
+        code: true
+    };
+
+    return function(md, opts) {
+
+        opts = Object.assign({}, defaults, opts);
+
+        md.options.highlight = opts.auto ? highlightAuto : highlight;
+        md.renderer.rules.fence = wrap(md.renderer.rules.fence);
+
+        if (opts.code) {
+            md.renderer.rules.code_block = wrap(md.renderer.rules.code_block);
+        }
+    };
+
+});