Allow a teacher/admin to edit a lesson

[amellie]

Dependency

Depends on #27

Story

As a Teacher or an Admin
I Want to edit an existing lesson
So That I can keep the lessons 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 lesson page (done in Allow a teacher or admin to create a new lesson #16), which allows users to update the module that the lesson is associated with, the lesson name, lesson description, and replace the lesson document
• Ensure that the validation is the same as what has been done in the create lesson page
• The edit page can be accessed from the lesson list page created in Allow a teacher/admin to see the list of lessons with controls #27. You need to modify the lesson 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 lesson list page (based on the module ID selected/edited) with a message "Lesson has been updated" (if successful) or show an error message if unsuccessful.