Store metadata on "up" migrations

[patricknelson]

Add new feature to store serialized metadata which is intended to be updated during up migrations. This will better facilitate down migrations so that information on what was changed can potentially be referenced when reversing said migrations.

Ideally the data here would be small. Best not to rely on the metadata field to retain the original values, but to only retain metadata about the values that were changed (e.g. which objects were updated).

Example: In creating a migration to convert a field of some (but not all) DataObject's, you may want to retain a list of all the ID's that were identified for change in the up migration that would otherwise not be possible to identify after the up migration has completed running. This makes it possible in the down migration to know how to reverse.

TODO: Determine storage limit. See MySQL datatype storage requirements.