[WIP] Add a few customizations for people wanting to selfhost

[kantenkugel]

This PR adds some customizations for people that want to self-host Butler for their own servers.

Things that were already added:

• Guild + Channel based whitelist for commands
• Possibility to opt out of the (or rather opt into a custom) Fakebutler listener (being able to have multiple applications to host the bot, but only one of them responding)

Stuff to think about:

• Commands
• Merge of [WIP] Move from notify blacklist to announcement mute role #30
• Items to version track
  • Opt-out of butlers auto-update routine