Feature - non unique email address on user accounts

On e3.23.0:

  • when you setup eramba, admin must have a valid email address
  • if you try creating a new account and use the same email as admin, you are not allowed to save

this is a bit annoying, we should let users have non-unique emails if they want to. I see no point for this not to happen.

Test case:

  • create two accounts with the same email, it should work

github: https://github.com/eramba/eramba/issues/4703