Save access_token in StorageManager

This will prevent the user from having to log in multiple times. It's
unclear to me how or when we will check if the access token is invalid.
Make the GoogleAuth class not require a callback on instantiation
Convert project to Android Studio / gradle

Goodbye, Eclipse.
Refactor bus map into its own class

This also includes a bunch of other junk updates to .idea files. If
these keep happening, they will be gitignored.
Change where the currently-selected bus lives

(it's going to be in BusMap, at least for now.)
Make GoogleAuth everything static

This is a weird refactoring, but I am doing it because it's
otherwise unclear to me how to share the state between LoginActivity
and MainActivity. GoogleAuth is basically a singleton class anyways.
Throw in Google Cloud Messaging sample code

This chucks in some sample code and integrates the registration of a
user into the app's startup process (asyncronously of course).

This will post the user's recipient_id to /users/, so the Rails app
can remember it for sending later!
Merge pull request #3 from ted27/master

STAND CLEAR, I THINK IT'S GONNA MERGE