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/highlight/github.css

@@ -0,0 +1,99 @@
+/*
+
+github.com style (c) Vasily Polovnyov <vast@whiteants.net>
+
+*/
+
+.hljs {
+  display: block;
+  overflow-x: auto;
+  padding: 0.5em;
+  color: #333;
+  background: #f8f8f8;
+}
+
+.hljs-comment,
+.hljs-quote {
+  color: #998;
+  font-style: italic;
+}
+
+.hljs-keyword,
+.hljs-selector-tag,
+.hljs-subst {
+  color: #333;
+  font-weight: bold;
+}
+
+.hljs-number,
+.hljs-literal,
+.hljs-variable,
+.hljs-template-variable,
+.hljs-tag .hljs-attr {
+  color: #008080;
+}
+
+.hljs-string,
+.hljs-doctag {
+  color: #d14;
+}
+
+.hljs-title,
+.hljs-section,
+.hljs-selector-id {
+  color: #900;
+  font-weight: bold;
+}
+
+.hljs-subst {
+  font-weight: normal;
+}
+
+.hljs-type,
+.hljs-class .hljs-title {
+  color: #458;
+  font-weight: bold;
+}
+
+.hljs-tag,
+.hljs-name,
+.hljs-attribute {
+  color: #000080;
+  font-weight: normal;
+}
+
+.hljs-regexp,
+.hljs-link {
+  color: #009926;
+}
+
+.hljs-symbol,
+.hljs-bullet {
+  color: #990073;
+}
+
+.hljs-built_in,
+.hljs-builtin-name {
+  color: #0086b3;
+}
+
+.hljs-meta {
+  color: #999;
+  font-weight: bold;
+}
+
+.hljs-deletion {
+  background: #fdd;
+}
+
+.hljs-addition {
+  background: #dfd;
+}
+
+.hljs-emphasis {
+  font-style: italic;
+}
+
+.hljs-strong {
+  font-weight: bold;
+}