Allow restricting of command usage per channel

[onebeastchris]

To combat the rise in "/ping" or "/uuid" command usage in channels such as #general, or #testers, this command adds two options to restrict command usage.

e.g.: With !settings set bot-channel <botchannelid> the bot channel can be set, where people will be directed to if their command usage is in a restricted channel (bot-free-channel).

With slash commands, the message would be sent in private.