Allow adding guild-level ResponseInfos

[5HT2]

• Re-add the ability to respond with a simple embed or title object.
• Ability to configure each property of a ResponseInfo.
• Setting the fn would require func(Response) functions to already be loaded (maybe via a plugin), but is still handy.
• A command to configure per-guild responses

See: https://github.com/5HT2/taro-bot/tree/impr/guild-response-39

[5HT2]

This is mostly blocked by the fact that like, guild responses call raw Go code and I don't want RCE as a service, so the best way to satisfy their requirements is a similar system that allows you to return embed json for a bunch of matched regexes?