rails4: fixing db migrations.

**Fix Migrations**:

* Do not use migrations for adding flags. Instead, repair tasks should be used, I think.
* In `AddDeviseToUserAccounts`, do not create duplicate columns, but change the existing ones of the `user_accounts` table. [See this SO answer](http://stackoverflow.com/a/12990129/2066546).

Trello: https://trello.com/c/Dlio0wG9/281-rails-4