Support for multi module setups

This CL adds support for building multi module apps
with proper context.

For library modules, we only generate base classes in the initial
compilation. We also generate a temporary BR file which does
not have final methods.

When final app is being generated, all layout binders, adapters
and Bindable information gets merged and all final classes
are generated in their appropriate packages.

This CL also adds support for Test runs and any
number of build variants.

Bug: 19714904
Change-Id: I9b50b54db05f3fa206eec33709d43c2ac94a9e5e