Only allow unique emails for user accounts

[4lm]

Closes #191.

@Bachibouzouk, please review this fix and merge on approval.

[Bachibouzouk]

@4lm - will this break things in an existing DB? Just want to make sure that I do not messup accounts in the online tool

Edit- It seems fine with my local DB. What would then happen to accounts that do share an email address? Are the surnumerous getting erased?

[4lm]

@4lm - will this break things in an existing DB? Just want to make sure that I do not messup accounts in the online tool

Edit- It seems fine with my local DB. What would then happen to accounts that do share an email address? Are the surnumerous getting erased?

I think the migration (for all accounts) will not happen (it will fail and abort without change) if two accounts use the same email. To fix this, if this case arises, someone would have to manually change the concerning email addresses in the database and re-run the migration.

But the chance that two accounts have the same email is IMO minimal anyway. And if so, are most likely duplicate accounts of the same person who registered twice by accident.

[Bachibouzouk]

Then I will perform a search if this is the case in the existing database before I merge this PR