Allow admin/teacher to edit a module

[amellie]

Dependency

Depends on #21 and #27

Story

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

Acceptance Criteria

• The edit capability should only be accessible by a teacher/admin
• The edit page should be similar to the create module page (done in Allow a teacher or an admin to create a new module #15), which allows users to update the module name and module description.
• Ensure that the validation is the same as what has been done in the create module page
• The edit page can be accessed from the module list page created in Allow a teacher/admin to see the list of modules with controls #21. You need to modify the module list page so that when a user click the Edit button, the user will be redirected to this edit page
• Upon submission of the edit page, the user should be redirected to the module list page with a message "Module has been updated" (if successful) or show an error message if unsuccessful.