LTI Authorisation

[Danwhy]

Users should be able to log in to Quodl through a link in Moodle.

• [x] Receive request to LTI endpoint
• [x] Validate request using OAuth
• [x] Check user type?
• [x] If user exists, log them in and continue to app
• [x] If user doesn't exist, prompt user creation (#667)
  • [x] Migration of users that exist in other authorisation flow
• [x] If module exists, join module and go to it
  • [x] new student
  • [x] existing student
• [ ] If module does not exist, create it (if user is lecturer)
  • [x] new lecturer
  • [ ] existing lecturer

part of #665