R1:aa481dba570d

Begin generating meaningful expected schemata

Summary:
Ref T1191. This lays some groundwork for generating the expected schemata, so we can compare them to the actual schemata and produce a meaningful diff.

- In general, each application will subclass `PhabricatorConfigSchemaSpec` and provide a definition of the tables it expects.
- This class has helper methods to mostly-automatically build table definitions for Lisk and (in the future) edges.
- When building expected schema, we specify a "data…