Fix FOUC on Firefox (#1728)

Firefox users will experience a flash of unstyled content on loading
various pages, this patch will fix this issue using Filament Groups
loadCSS library to asynchronously load the CSS responsible for the FOUC.

Will fix #1698.

Signed-off-by: Sondre Nilsen <[email protected]>

Author: sondr3

public/assets/librejs/librejs.html

@@ -36,6 +36,15 @@
         <td><a href="https://github.com/Ranks/emojify.js/archive/1.1.0.tar.gz">emojify-1.1.0.tar.gz</a></td>
       </tr>
       <tr>
+        <td><a href="/js/libs/loadCSS.min.js">loadCSS.min.js</a></td>
+        <td><a href="https://opensource.org/licenses/MIT">MIT License</a></td>
+        <td><a href="https://github.com/filamentgroup/loadCSS/archive/v1.3.1.tar.gz">loadCSS-1.3.1.tar.gz</a></td>
+      </tr>
+      <tr>
+        <td><a href="/js/libs/cssrelpreload.min.js">cssrelpreload.min.js</a></td>
+        <td><a href="https://opensource.org/licenses/MIT">MIT License</a></td>
+        <td><a href="https://github.com/filamentgroup/loadCSS/archive/v1.3.1.tar.gz">loadCSS-1.3.1.tar.gz</a></td>
+      </tr>
         <td><a href="/plugins/dropzone-4.2.0/dropzone.js">dropzone.js</a></td>
         <td><a href="http://www.freebsd.org/copyright/freebsd-license.html">Expat</a></td>
         <td><a href="/plugins/dropzone-4.2.0/dropzone.js">dropzone.js</a></td>

public/js/libs/cssrelpreload.min.js

@@ -23,7 +23,8 @@
 {{end}}
 
 	<link rel="shortcut icon" href="{{AppSubUrl}}/img/favicon.png" />
-	<link rel="stylesheet" href="{{AppSubUrl}}/assets/font-awesome-4.6.3/css/font-awesome.min.css">
+	<link rel="preload" href="{{AppSubUrl}}/assets/font-awesome-4.6.3/css/font-awesome.min.css" as="style" onload="this.rel='stylesheet'">
+	<noscript><link rel="stylesheet" href="{{AppSubUrl}}/assets/font-awesome-4.6.3/css/font-awesome.min.css"></noscript>
 	<link rel="stylesheet" href="{{AppSubUrl}}/assets/octicons-4.3.0/octicons.min.css">
 
 {{if .RequireSimpleMDE}}
@@ -53,7 +54,8 @@
 {{end}}
 	<style class="list-search-style"></style>
 
-	<!-- Open Graph -->
+	<script src="{{AppSubUrl}}/js/libs/loadCSS.min.js"></script>
+	<script src="{{AppSubUrl}}/js/libs/cssrelpreload.min.js"></script>
 {{if .PageIsUserProfile}}
 	<meta property="og:title" content="{{.Owner.Name}}" />
 	<meta property="og:type" content="profile" />