cookies: Use js-cookie to read and write cookies

Rather than reinvent the wheel, use a well-tested library to parse and
write cookies. This should also help prevent XSS vulnerabilities
because the library handles special characters such as semicolon.

src/node/utils/Minify.js

@@ -44,12 +44,13 @@ var threadsPool = Threads.Pool(function () {
 }, 2)
 
 var LIBRARY_WHITELIST = [
-      'async'
-    , 'security'
-    , 'tinycon'
-    , 'underscore'
-    , 'unorm'
-    ];
+  'async',
+  'js-cookie',
+  'security',
+  'tinycon',
+  'underscore',
+  'unorm',
+];
 
 // Rewrite tar to include modules with no extensions and proper rooted paths.
 var LIBRARY_PREFIX = 'ep_etherpad-lite/static/js';

src/node/utils/tar.json

@@ -17,6 +17,7 @@
   , "pad_connectionstatus.js"
   , "chat.js"
   , "gritter.js"
+  , "$js-cookie/src/js.cookie.js"
   , "$tinycon/tinycon.js"
   , "excanvas.js"
   , "farbtastic.js"