SDI: allow filtering users by email and name

[dwt]

The users list in the SDI is very useful - however it becomes considerably less useful as soon as there are many users, because finding the right one without clicking through all users is quite painful.

Therefore, I propose that the filter function is extended to allow filtering by email and name to quickly find the right user to change something.

Chatting with @joka it seems that just showing these additional columns in the SDI will probably do the trick.

[xi]

@dwt the column are now available. Filtering is not affected, though. Please reopen of you still consider this an issue.

[joka]

repopen to implement sorting and filtering by email/user name.