Many changes leading up to GA shallow water test

- Create centralized test suite
- Create PDESystem/BVP/IBVP hierarch
- Expose scalarization as a system-level service
- Move onto GA infrastructure in pymbolic
  (shared with pytential)

Fixes #10.
Remove debug print
Merge branch 'master' of github.com:ibvp/ibvp

Conflicts:
	examples/wave.py
	ibvp/language/symbolic/mappers.py