Add better support for turning mods on/off

* Make the Minecraft "mod" enabled at all times
* Sort the list of mods to move required mods to the top
* Automatically enable a mod which has a recipe selected (e.g., from
  a query param)

src/scripts/constants.coffee

@@ -35,6 +35,10 @@ exports.Opacity = Opacity = {}
 Opacity.hidden  = 1e-6
 Opacity.shown   = 1
 
+exports.RequiredMods = [
+    'Minecraft'
+]
+
 exports.UrlParam        = UrlParam = {}
 UrlParam.quantity       = 'count'
 UrlParam.recipe         = 'recipeName'