[x] When an existing Quodl user signs in via Moodle they are taken to the /merge-accounts screen, where their email is already filled in and they have to re-enter their password to confirm they want to merge accounts.
[x] When an account has been merged, it should redirect to the correct module.
[x] Password is kept, even when accounts have been merged
/merge-accountsscreen, where their email is already filled in and they have to re-enter their password to confirm they want to merge accounts.