Add ClientData class for data that is only local to the device.

Also added a test class for the current implementation.
Fix test compilation so that I can run the ClientData tests.
Moved DataStore files into data package.
Use ClientData for username, and so remove it from LocalDataStore and interface.
Fix tests.

Tests had to be converted to ActivityInstrumentationTestCase2 so that we could get a context.
Merge pull request #71 from stephenjust/client-data

Some work towards LocalDataManager: ClientData class