Adding and/or fixing unit tests around data migration.

One weird thing: the ATDataModelv2.sqlite file appeared to have been corrupt/un-openable.

I added a bunch of verification around the data manager so that internals were visible for unit testing. This was to ensure that things like migration happened, database was deleted, migration failed, etc.
Merge branch 'MigrationFix' of github.com:apptentive/apptentive-ios into MigrationFix