Warn user when their dump is newer than their test_data environment by persisting dump metadata (time, user, git ref) and checking at boot

[searls]

If an application_test_data database exists and is non-empty, rake test_data:load will fail. But it may not be obvious to the user if the test_data in git is newer or older than what's in the test_data database.

Saving some meta data in an ar_internal key/value pair might allow for better decision-making about when to blow away the database vs overwrite the dump