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 type", like "epoch". This is the type of data the application stores in the column, from the application's point of view. The SchemaSpec converts this into the best avilable storage type: for example, "text" will translate to utf8mb4 if it's availalbe, or binary if not. This gives us a layer of indirection to insulate us from craziness.

Test Plan: See screenshots.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10497