Use HIBERNATION_STATUS in header panel
Nyx's header panel polls the control port for hibernation information. Tor 0.2.9.x adds a new HIBERNATION_STATUS event we can listen to instead to cut down on the GETINFO queries we make.
This is a very small change to our load on the control port (one GETINFO request every five seconds), so not really a high priority. If somebody wants to do this then great, but I'll probably wait until tor versions prior to 0.2.9.x are deprecated to avoid the headache of 'if version x to this, if y do that'.