thank sub gifters

[zephyrtronium]

Robot should thank people who gift her subs. Look for USERNOTICE with msg-id either "subgift" or "anonsubgift" and with msg-param-recipient-user-name equal to the bot's lowercase username or msg-param-recipient-id equal to the bot's userid if we get that at some point. Additional relevant docs: https://dev.twitch.tv/docs/irc/tags#usernotice-twitch-tags

Thank with a chat message, possibly a special set of emote options for doing so, maybe a big chunk of affection.