Change login credentials

**Is your feature request related to a problem? Please describe.**
- Users on I-analyzer cannot change their email address; they have to register a new account.
- If you registered through your university and then lose access to that account (because you graduate, switch to a different job, a different academic institution, etc.), you permanently lose access to your I-analyzer account.

**Describe the solution you'd like**
- [ ] Allow users to change their e-mail address through the settings menu.
- [ ] If a user logs in via SAML, allow them to convert their account to a "normal" account by setting an e-mail address and password.

**Describe alternatives you've considered**

We could also focus on features like #1065 which allow users to transfer account data.