FEATURE: Allow selection of highlight js languages

PERF: stop loading highlight js on load

To get latest highlight js run bin/rake highlightjs:update

app/assets/javascripts/main_include.js

@@ -4,11 +4,6 @@
 // Pagedown customizations
 //= require ./pagedown_custom.js
 
-// This is a BUG we should fix
-// it is only required here cause preview is not loading it using LAB
-//= require highlight.pack.js
-//
-
 // Stuff we need to load first
 //= require ./discourse/lib/load-script
 //= require ./discourse/lib/notification-levels