Removes jQuery dependency

jQuery Rails is now at v3, so forcing a lower version means that some
users will run into dependency conflicts when installing CASino
(especially Rails 4 users)

Additionally, not only do some users not use (or want) jQuery in their
application, CASino isn't using that much javascript to necessitate
pulling in all of jQuery.

This updates the javascript in two ways:

* Replaces the auto-focusing of CASino elements with the `autofocus`
  HTML5 attribute
* Replaces the jQuery-specific javascript that automatically logs a
  user in when a TGT is already present with native DOM calls inlined
  directly in the login form so that it is always present, regardless
  of how the parent application has configured its layouts.