Prevent duplicate alarms from being created via intents

Bug: 26644030

A duplicate alarm is one that matches all of the following fields:
- hours
- minutes
- repeat days
- message
- vibrate
- ringtone

Note: duplicate alarms can still be created through the user interface.
This is mostly allowed because the user interface for describing the
duplication would be awkward.

Change-Id: Ia8ac16ca2041700625a34df4fa2948fe9d774e4c