Progress on the char sheet layout. Started work on sqlite db.

- Added Gson library for quick and easy serialization to JSON.
- Added Json interface.
- Updated Attributes and CharSheet to implement the Json interface and
utilize Gson to handle the conversion to and from JSON.
- Added AbstractData class: Adds an id member variable with
getter/setter.
- Updated Attributes and CharSheet to extend AbstractData
- Added DbOpenHelper which extends
android.database.sqlite.SQLiteOpenHelper