Customize moocfi id from web ui

[nygrenh]

• [x] Edit option to form
• [x] bullet point to teacher info that says points wont by synchronized to moocfi
• [x] Option to course creation
• [x] Validate uniqueness in tmc db
• [x] Validate that a course with given id exists in mooc.fi

[Redande]

Pull request https://github.com/testmycode/tmc-server/pull/533 adds this customization