Having multiple accounts with the same email address breaks the login

[fer-rum]

Steps to reproduce:
Add an organizer account with a given email address.
Add a Tutor account with a different name but the same email address.

Upon Login you now get an Authentication error.

Proposed solution:
Disallow re-use of already taken email addresses or switch to alternative login via a given unique username. If both represent the same person, allowing a user to have both roles can be considered, but is not mandatory.

[JustusAdam]

Wouldn't it be smarter to instead of having separate user objects for tutors and organisers have just a general user object with either some roles denoting wether it is a organiser or tutor or some boolean basically describing the same thing?

Otherwise I'll be a pain to be a tutor and a organiser at the same time.