More fixes towards #912 (my proposed alternative to PR #917)

Here's my proposed alternative to PR #917 that does not include a lot of extra if logic. It simply makes use of `UserID` which is unique throughout the uptime of the server for bots as well as players. It was also hook into as FAdmin.FindPlayer already accepts User IDs which means that Steam IDs will still work - I did not touch the commands themselves.

This fixes all issues connecting to #912.