clock: modify alarms creation/edit logic.

clock: modify alarms creation/edit logic.

Implement logic included in UX guideline page 13.

Now when alarm is added app first checks if alarm with
same time and name exists, if yes it updates it accordingly,
if no - creates new alarm.

When alarm is modified, app first checks if alarm with
same name and time exists, if yes it updates it and deletes
edited alarm, if no - updates existing alarm.

Change-Id: Ie179d35de895ac702898202ee72fc745165c2d53