Implement Hipchat setting

Hi,
could you implement Hipchat message_format ( seems that now is used "default" which is html ) ?
We need message_format = text .
More info: https://www.hipchat.com/docs/apiv2/method/send_room_notification
thanks.

Start by tracing the Hipchat notification integration and its configuration path, then compare the current request with Hipchat's send_room_notification documentation linked in the issue. Done means the Hipchat message_format can be set to text instead of always using the current default.

Written by the indexing model from the issue text.