Fixes duplicated names in alarm time constraints

Currently, an alarm can have multiple time constraints
with the same name. Consequently the constraints aren't
uniquely identifiable and cannot be edited correctly.

This patch adds duplicate checking.

Change-Id: I6654e13b249db53c2107b43fe36ddacedf67be67
Closes-bug: #1293994
Merge "Fixes duplicated names in alarm time constraints"