Implement a !rq similar to how Limnoria does it

[NetSysFire]

@examknow specifically asked me on IRC to report this one. "!rq" stands for random quote in Limnoria.

Steps to reproduce

1. Be in a fun channel.
2. Try to make the bot emit a random quote that was grabbed in this channel.
3. ,quote on its own requires an argument and ,quote <#channel> will return [Quotes] No matching quotes
4. Be sad.

Expected behavior

,quote on its own would emit a random quote grabbed in this channel or namespace.

Make the latter one configurable perhaps. In e.g a fictional ontopic "#linux" channel, you'd want a random quote to only consist of ones grabbed in that channel, not the potentially inappropriate ones from e.g the offtopic channel. "#linux-offtopic" however would be just fine with any public quotes from the entire #linux-* namespace.

[examknow]

I think we should limit random quotes to inside a single channel context. If nothing else, this will avoid accidental exposure of private data to public channels.

[examknow]

Perhaps the channel-quotes settings should also be defaulted to on for the same reason

cc @jesopo - thoughts on this?