Added email check - users cannot share email addresses

In older GpsGate installations, a Site Admin user has been allowed to share an email with other users on the system.

We have now added a check to avoid that to keep the server neat and clean.

You may get this error when you try to add an application:

Application could not be created: Error: Email john@example.com already belongs to username XYZ

There are 3 possible ways:

1. Click on the Advanced button and select/create a new administrator for this application.

2. Change/remove the email address from the Site Admin user in Site Admin > Applications > Site Admin Users > (select the user) > E-mail.

3. Login to the application and change the email from the user that currently owns it.