updated hipchat service to have quiet comments and labels

This is a patch for issue #902 trying to make the hipchat integration a lot less verbose.
We tried moving to their new add-on but it was even more verbose...

This is my first time working with github-services so feel free to point anything out that I have missed.
I wasn't clear if I needed to do anything else to get the options appearing in the control panel on github itself apart from add them to the hipchat.rb file
Because of my previous mention about these not actually being events, you'll need to actually look at `event.to_s =~ /issue/` as well as the payload's `:action` attribute to see if it's a label/assignment or not.