[LogMessage] Add model and DB level validations.
[Owner] Add model and DB level validations.
[Session] Add model and DB level validations.
Disallow NULL at DB level for all created_at fields.
Normalize schema back to one migration.

Created with:

```
$ rm db/migrations/*.rb
$ bundle exec sequel -d postgres://localhost/trunk_cocoapods_org_test > db/migrations/001_create_initial_tables.rb
```
[API] Don't create an Owner/Session in case an error occurs.
[PodVersion] Move unique validation error to `name' key.
[Owner] Validate email domain has valid MX records.
[API] Handle all errors in one place and in a JSON friendly way.
Some misc NewRelic things.
[TODO] Update
[API] Remove inline error handling.
[API] Update owner's name on subsequent registrations, if specified.
[SubmissionJob] Re-raise exceptions that occur while performing work.
Make tests green.