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/cssrelpreload/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) @scottjehl, 2016 Filament Group
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

public/vendor/plugins/cssrelpreload/cssrelpreload.min.js

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+/*! loadCSS rel=preload polyfill. [c]2017 Filament Group, Inc. MIT License */
+!function(a){if(a.loadCSS){var b=loadCSS.relpreload={};if(b.support=function(){try{return a.document.createElement("link").relList.supports("preload")}catch(b){return!1}},b.poly=function(){for(var b=a.document.getElementsByTagName("link"),c=0;c<b.length;c++){var d=b[c];"preload"===d.rel&&"style"===d.getAttribute("as")&&(a.loadCSS(d.href,d,d.getAttribute("media")),d.rel=null)}},!b.support()){b.poly();var c=a.setInterval(b.poly,300);a.addEventListener&&a.addEventListener("load",function(){b.poly(),a.clearInterval(c)}),a.attachEvent&&a.attachEvent("onload",function(){a.clearInterval(c)})}}}(this);

public/vendor/plugins/cssrelpreload/loadCSS.min.js

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+/*! loadCSS. [c]2017 Filament Group, Inc. MIT License */
+!function(a){"use strict";var b=function(b,c,d){function e(a){return h.body?a():void setTimeout(function(){e(a)})}function f(){i.addEventListener&&i.removeEventListener("load",f),i.media=d||"all"}var g,h=a.document,i=h.createElement("link");if(c)g=c;else{var j=(h.body||h.getElementsByTagName("head")[0]).childNodes;g=j[j.length-1]}var k=h.styleSheets;i.rel="stylesheet",i.href=b,i.media="only x",e(function(){g.parentNode.insertBefore(i,c?g:g.nextSibling)});var l=function(a){for(var b=i.href,c=k.length;c--;)if(k[c].href===b)return a();setTimeout(function(){l(a)})};return i.addEventListener&&i.addEventListener("load",f),i.onloadcssdefined=l,l(f),i};"undefined"!=typeof exports?exports.loadCSS=b:a.loadCSS=b}("undefined"!=typeof global?global:this);