Moved vendored js/css into public/vendor and documented sources (#1484) (#2241)

* Cleaning up public/ and documenting js/css libs.

This commit mostly addresses #1484 by moving vendor'ed plugins into a
vendor/ directory and documenting their upstream source and license in
vendor/librejs.html.

This also proves gitea is using only open source js/css libraries which
helps toward reaching #1524.

* Removing unused css file.

The version of this file in use is located at:
  vendor/plugins/highlight/github.css

* Cleaned up librejs.html and added javascript header

A SafeJS function was added to templates/helper.go to allow keeping
comments inside of javascript.

A javascript comment was added in the header of templates/base/head.tmpl
to mark all non-inline source as free.

The librejs.html file was updated to meet the current librejs spec. I
have now verified that the librejs plugin detects most of the scripts
included in gitea and suspect the non-free detections are the result of
a bug in the plugin. I believe this commit is enough to meet the C0.0
requirement of #1534.

* Updating SafeJS function per lint suggestion

* Added VERSIONS file, per request

public/vendor/plugins/codemirror/mode/diff/diff.js

@@ -0,0 +1,47 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: http://codemirror.net/LICENSE
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+"use strict";
+
+CodeMirror.defineMode("diff", function() {
+
+  var TOKEN_NAMES = {
+    '+': 'positive',
+    '-': 'negative',
+    '@': 'meta'
+  };
+
+  return {
+    token: function(stream) {
+      var tw_pos = stream.string.search(/[\t ]+?$/);
+
+      if (!stream.sol() || tw_pos === 0) {
+        stream.skipToEnd();
+        return ("error " + (
+          TOKEN_NAMES[stream.string.charAt(0)] || '')).replace(/ $/, '');
+      }
+
+      var token_name = TOKEN_NAMES[stream.peek()] || stream.skipToEnd();
+
+      if (tw_pos === -1) {
+        stream.skipToEnd();
+      } else {
+        stream.pos = tw_pos;
+      }
+
+      return token_name;
+    }
+  };
+});
+
+CodeMirror.defineMIME("text/x-diff", "diff");
+
+});