DeskClock: Recreate alarms DB on downgrade

This fixed the cm10 to cm10.1 transition (from version 7 to 6)

Change-Id: Ia30915e8c4ebc36b191b5a876acbc8cb779b6689
JIRA: CYAN-1188
Issue: https://jira.cyanogenmod.org/browse/CYAN-1188
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>