E1482. Rewrite Project E1401

Project E1482 includes merging of E1453 and refactoring assignments_controller using a form object. We have made assignments_controller using form object. Please provide your comments
Instead, please make an idempotent data migration in `db/data_migrations`. That means you should be able to run it over and over again without negative consequences. [Here](https://github.com/expertiza/expertiza/blob/rails4/db/data_migrations/alter_max_team_size.rb) is one I wrote, as an example.