Using gradle project structure

Moved:
src -> src/main/java
res -> src/main/res
assets -> src/main/assets
Basic unit testing - not tested yet

Was not tested because this was created without internet connection -> dependencies could not be resolved
Unit tests are working.

The SanityTest was now adapted not to fail. Used as a proof that unit tests are working.
Added robolectric.

To write more tests.