Add alarm silence #7

Once alarm is occured, watcher has an option to silence it for certain amount of time. Time spans available: 15 min, 30 min, 60 min, 90 min, 120 min.
Silence applies only to the current alarm type, so if watcher silences regular alarm, urgent alarm (if any) will still be audible. And it's possible to mute urgent alarm too using the same UI.