plugins/hipchat-v2: add integration with hipchat v2

Fixes #113 (HipChat API v2 Support)

So this code does work. However, when I test it locally (by pressing
"Test notification") it fails. The reason is that nothing is
running on localhost:7000 (connection refused). I'm not sure
what there should be.
I must have accidentally deleted it, while testing. Sorry.