Send warning about inactive users

It would be nice to get warned about users inactive after X months. In order to decide about deleting them, because I am not using SSO yet.

Also nice would be to resend an invitation or email if the user passes that specific time, so he would need to go to the e-mail and click the link to be able to access the project again. That would block users who left the company to access the project, leading to security issues.