Re-enable Gist support, add support for channel passwords

In my testing with the 11.4.4 Omnibus Chef client I found that Gisting works perfectly fine, so I've re-enabled it. If it's still broken under some of your environments, I'm willing to rework this to use an attribute to decide whether or not to attempt the Gist.

I also added support for channel passwords; my organization has a private channel that I want it to announce to, so that was something that we needed to do.

Thanks for your great work, this has been very helpful!