Allow admin/teacher to delete a module

[amellie]

Dependency

Depends on #21 and #27

Story

As a Teacher or an Admin
I Want to delete an existing module
So That I can keep the modules up to date

Acceptance Criteria

• The delete capability should only be accessible by a teacher/admin
• Deletion can be done from the module list page created in Allow a teacher/admin to see the list of modules with controls #21, by clicking the Delete button. The module list page should be updated to allow this control
• When a module is deleted, ALL of its associated lessons and submissions should be deleted. In the database level, deleting a module should result in the automatic deletion of the lessons AND submissions. This can be done if you set DELETE CASCADE on the modules table as explained here
• The lesson documents and submission documents associated with the module should be permanently deleted from the server as what's done in Allow a teacher/admin to delete a lesson #30
• Ensure that users can confirm Yes/No if they REALLY want to delete the module (after clicking the Delete button). Please also mention that deleting this module will result in the deletion of all of its associated lessons and submissions and the action cannot be reversed
• Upon deletion, the user should be redirected to the current module list page with a message "Module has been deleted" (if successful) or show an error message if unsuccessful