Fixing issue 446: R.java for aar libraries doesn't generate in some cases

Currently R.java for all transitive aar dependencies generates only if current artifact has APK packaging.
In other cases R.java doesn't generates for all transitive aar dependencies, so we cannot use resources from aar in other aar or in apklib dependency.

Solution:
I've added generation R.java(based on R.txt) for all aar transitive dependencies(even if current artifact packaging is not APK)