Candidate fix for crashes related to a bad migration and leftover SQLite WALs.

The current theory being that while we migrated a store, we left over the WAL and SHM SQLite files, which resulted in database corruption.

Since the corruption involves missing columns in SQLite, we can try to detect that and wipe the database.

We also want to ensure that messages sent by the user are restored as such, and do so in ATGetMessagesTask.
More reliable fix in the face of crashes with previous approach.
Fix for memory leak.
Adding canary for database setup.
Pesky “/“
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
Updating podspec.