stub out core module

This request is to stub out the core functionality required by an android module which would be shared between the various deployed apps.

At present this set is limited to the wear module (to be completed in another pull), and the app.

The workflow I was thinking was as core functionality is required by features in the wear app, they would be moved from the current ```onebusaway-android``` module into the ```core``` module to keep the core module as lightweight as possible.
This looks good to me.