Decouple the viewing from the generation of the PDG

Might be useful for testing the PDG in the future.

See #30.
Update WALA submodule

This contains our change to make com.ibm.wala.cast.java.test public.

See #30.
Add skeleton for PDG unit tests

See #30.
Add Java60RegressionExclusions file to ignore certain libraries

See #30.
Update WALA submodule

Remove unused Collection<String> sources parameter

See #30.
First pass at creating test suite

The test is failing but at least the infrastructure is sound.

See #30.