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
You can have a method in `@assignment_form` which creates the node: `@assignment_form.create_assignment_node`, for example, which calls `create_node` on the assignment, if it isn't nil.