Set a PM string for role toggling commands

[MorrisTheHorris]

Add a generic way to set a string that the bot PMs to users after they use commands like !meta, !weeb etc. listing whichever different rules that may apply to that restricted channel. Then, !accept could be moved from MEE6 and the rule blurb can be PMed.

[VineBalloon]

Could be done in the rewrite, adding this issue to the project.