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.
Merge remote-tracking branch 'upstream/master'
Add server-wide silence

40 minutes of hardcoded silence removed. Now to ACK the alarm client has to select silence time (possible values: 20, 30, 40, 50, 60 minutes). After that selected silence time and corresponding alarm type (urgent/regular) is being transferred on the server with ACK event. Server then uses these settings to postpone corresponding alarm independently.
Remove test code
Update README.md

Added link to wiki.
Update package.json

Fixes issue #16
Add mutual exclusion of alarms
Merge pull request #9 from troggy/master

Add alarm silence #7
Update package.json

Fixes #18.