Who is using my user id? New endpoint.

[crspybits]

When a user has previously invited users to the system and those users joined with non-owning accounts, and the user is about to delete themselves from the system, it could be useful for them to know if/howmany/which users remain on the system making use of their creds-- i.e., to upload files. This could inform their decision about whether or not to remove themselves.