migrating webhook to use room_message instead of room_notification

[csnate]

I don't know if anything has changed with HipChat in the last year, but when I integrated this plugin the Name wasn't come through on the webhook message. I noticed that the event that was being registered with the HipChat webhook was "room_notification", which wasn't getting fired with a normal message. So, I switched the webhook event over to "room_message" (which has a different response contract) and then updated the contracts to get the correct Name. Works correctly now.