Removed necessity to subclass SugarApp

Like described in #44 it is sometimes not feasible to subclass SugarApp. In that cases it would be better to have some kind of a static initialiser do get things running.

In the implemented variant it is just needed to initialize Sugar by calling `SugarApp.init(Context)` when the app starts up. To close the database we also need to call `SugarApp.terminate()` to indicate that the database should be closed.
We won't be needing this with the recent changes to https://github.com/satyan/sugar/commit/02e1d4974d55733c3857736c832f3f948b26fa2c. I'll handle culling this out of the PR before I merge your work in.