[#7527] Allow different users to claim the same email address + tests
[#7527] Added EmailAddress data migration
[#7527] Bugfixing
[#7527] Replaced the migration with a raw mongo migration
[#7527] Split the migration into 3 steps
[#7527] Flush email address
[#7527] Bugfix for migrations to prevent duplicates
[#7527] Fixed unit tests