Move to consistent data_migrations

[teadur]

We have been using different methods how we migrate data in our database.

1. At first data_migrate gem was used ( https://github.com/internetee/data-migrate )
   That introduced db/data directory with some migrations and data_migrate table (what was removed in 62ec30c )
   Our Gemfile still requires data_migrate.
   If we want to use data_migrate gem we should move to current version of it ( https://github.com/ilyakatz/data-migrate )

2. We have migrated some data inside normal activerecord migrations
   38f967a

3. We have written some data migrations as rake tasks ( Very hard to figure out the correct ordering / at what point of time they should be applied )

https://github.com/internetee/registry/search?q=data_migrations&unscoped_q=data_migrations

We need to figure out how we want to migrate data and stick to one method.
I propose we upgrade data_migrate gem and use only that for data related migrations.

[vohmar]

fixed by #1539