Merge pull request #9 from jusa/pa4

Role-based listening time notifier.
[mainvolume] Send HighVolume signal always on mode and call mode change.
[mainvolume] Reset volume to safe level on startup.

If volume is set on accessory with HighVolume defined to a level that is
not safe, when restarting mainvolume module and selecting those steps
for the first time, reset volume to a safe step.
[mainvolume] Add CallState signal.