The main thrust of this PR is to make the Push APIs follow the
factory/config pattern of Pipe, Authentication, and Store.
Here is a before and after gist :
https://gist.github.com/secondsun/b01c3446095fb29a85e3
Here is a link to the PR:
https://github.com/aerogear/aerogear-android/pull/94
I've also included a small bit of API cleanup. For instance the
PushRegistrar now keeps a reference to the PushConfig so you don't have
to pass it into register and unregister. Also, I extracted an interface
from the Registrar object so in the future we can add support for non
GCM push services. (There are also two JIRAs to support that eventual
goal).