Set up the singleton properly

* Moved bus registration/dereg to base fragment
* Used static calls to get reference to the activity
* Added convenience function to application and used in the base fragment
* Added activity tests
REFACTOR: Removing IDEA project files
REFACTOR: Updating to a modern version of Android
Added rotation handling

* Stored displayed value on the Activity and restored
* Activity only creates calculator state fragment when it needs a new one
* Added logging of save/restore events
* Removed portrait only orientation in the manifest
* Removed unnecessary super calls in the fragment view creation
Added tests for text on each button
REFACTOR: Small simplification
Simplified styles, wasn't using BaseButton on Number and duplicating width, height, and margin attributes.
Removed the base text from the display view since it isn't using either of the base properties.
Removed hardcoded whie, used android's white instead