Support application code and libraries for android applications

Created by: saleehk

Ant and Gradle have a concept of "application code" and "libraries", but Buck only has libraries. The application code gets one special privilege, however: its resource ids are constants, which means that they can be used in switch statements and annotations.

This would able things like this with ButterKnife:

@InjectView(R.id.button1) Button button1;
@InjectView(R.id.button2) Button button2;