User:Salvatore Ingala/RL2 integration

TODO list:

• Integrate remaining changes from salvatoreingala branch to RL2 branch
  • Gadget.php
  • Hooks
  • GadgetsMainModule
  • ext.gadgets.preferences
• Port integrated code to new backend
  • API modules
  • GadgetOptionsResourceLoaderModule (maybe)
  • Hooks
  • possibly more stuff, keep poking until the fatals go away
• Move JSON blob in MediaWiki:Gadget-foo.preferences to an element of Gadget definition:Foo.js
• [Roan] Review jquery.formBuilder, GadgetPrefs
• Fix test cases for new backend