Make 'refresh token' work again
Fix check for already used email when changing email

storage::findAndGetUser() was throwing an Exception when no
entries were found. Fixed by using isRegistered() first.
Fix renameEntry()

Binding as admin was required in order to be able to write
Add missing string
Check if the requested email address is already used

This commit checks the mail attribute in addition to
irisMailAlternateAddress..

Also performs the check before generating a token for the request.