More info schema restructuring:
+ Arrange for info schema tables to be backed by one of two different class hierarchies, the computed and direct hierarchies.
  Try to make everything behave the same way.  The backing class hierarchies are the adapters for the info schema columns and
  tables.
+ Changed a bunch of class names to be less unwieldy.
+ Add a new builder that replaces existing tables as they are migrated.
+ Added more state around emitting table instances in the emitter.

The upgrade is now broken, will address after migrating some more tables.