Request proximity based screen blanking from powerd
This change adds a PowerDAudioModeMediator which will react to the used audio output. If bluetooth or speakers are used for a call it will make sure the display is not turned off because of proximity events. This is done by calling the PowerD Dbus interface methods enableProximityHandling and disableProximityHandling accordingly.
Additionally C++11 is activated. Fixes: 1353560, 1367341
Approved by: Ricardo Salveti, PS Jenkins bot, Tiago Salem Herrmann