Mirror channels more closely

[jvperrin]

Ideally we'd like to mirror channels and topic changes from IRC <-> Slack. This means creating new channels when needed on both Slack and IRC, which looks like it should be possible through the Slack API with channels.create and channels.archive and by joining a new channel on IRC and potentially registering it with ChanServ.

Hopefully this works on Slack's end, since previously the bot had to be manually invited to a channel, but maybe if it creates the channel itself then it will auto-join it? If it's created on Slack, then the bot might have to be invited to have it be properly mirrored on IRC.

We also don't want to mirror certain channels if they are private, like IRC's #services or any private channels on Slack unless we add access restrictions with ChanServ. Seems like it might be prone to issues too since each user bot doesn't use NickServ currently (see #6 for that). Seems like it would be pretty cool to be able to have private channels if we want and have those properly mirror.

[jvperrin]

So changing the topic on Slack works fine with the bot user, but changing the topic on IRC requires the user changing it to have more permissions (chanop or whatever it is set to with config). If the slack-bridge user is given chanop status, this helps, but it makes all the other slack users also get chanop, since they are all authenticated on the same nickserv account (as aliases). We also probably wouldn't want anyone to be allowed to change the topic, since it's fully public. This means that mirroring topic changes from Slack -> IRC is unlikely to work, but since they mirror already from IRC -> Slack already, I think that's good enough.

I think all that's really left on this now is channel creation. When a channel is created on IRC, I don't think we'd necessarily want it created on Slack too, since it might be private, but when one is made on Slack and the irc-bridge bot is invited, then obviously we should mirror it. Private channel support would also be cool, but would require more fiddling with IRC stuff than we might want to do.