Remove unused envOfInterpretation.
Remove some unnecessary definitions.
Implement liftEngine to run EngineM computations in Interpretation.
Migrate genBuiltins to EngineM.
Implement partial runInterpretation, migrate init*.
Migrate UniProcessor to EngineM.
Migrate virtualizedProcessor to EngineM.
Migrate debugDispatch to EngineM.
Migrate runProgram to EngineM.
Migrate runNetwork to EngineM.

It now returns a potential error status, to be handled one level up. It still
needs to be determined which top-level entry points into the system should be
exposed, and where.

The system now builds through the entire toolchain.