Monster Munch (Add Monster Model to add more coverage for different relationship types.)

This is mostly a starting point model for some relationship fixup/change detection work. There are some TODOs for somethings that don't work yet. I updated relational type mapping to support nullable types and simple enum mapping.
Share and Enjoy! (Share common TypeExtensions code)
Migrations: Added HistoryRepository, MigrationAssembly, Migrator, MigrationScaffolder classes.
Made updates and wired up functionality as necessary. Added unit tests.