Add restart command (enhancement)

[lost-hope]

Maybe add a restart command to restart the bot, if it gets stuck on a error like "Command raised an exception: FileNotFoundError: [Errno 2] No such file or directory". (if that is possible)

Limit the use to a certain role like the Moderators, so there is a less likely chance of a malicious use.
That way the bot can be used, even if you are away for a longer time.