Added click listeners to number buttons

* Promoted layout to a field
* Created a click listener for number keys
* Posted number event to the bus
* Added NumberEvent, extends BE and takes a String
* Moved BaseEvent into the events package
Handling the number event in Activity

* Register/unregister with the bus
* Subscribe to number events
* Moved the click listener
Added testing

* Added base fragment
* Extending base fragment
* Created test fragment, capture events
* Verify events posted, refactored tests to support