Satellizer supports Opauth

Satellizer now supports using Opauth on the serverside.

Notes: 
* ```UsersController::opauth``` implementation is messy and proof of concept.
* ```UsersController::opauth``` only supports Opauth 2.0 strategies atm (1.0 should be very easy, though)
* Comment out ```return popup.pollPopup();``` in satellizer-opauth.js:551 to stop the auth popup from closing (for easier debugging of ```UsersController::opauth```)