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
Try to keep your methods short. Look at [this form object](https://github.com/expertiza/expertiza/blob/rails4/app/models/student_task.rb) I created a few years ago as an example of how to use methods inside of other methods to shorten overall method length.