EmergencyNumber enhancement

1) Add Database source for EmergencyNumber
2) add mergeEmergencyNumber for merging two emergency numbers
3) enable Listener.EmergencyNumber enhancement
4) no need to pass any parameter to PhoneNotifier
5) modify API documentation
6) deprecate PhoneNumberUtils.isEmergencyNumber
7) modify API documentation for security exception and backward
compatibility
9) introduce some utils in EmergencyNumber for merging number purposes
10) add mnc into EmergencyNumber

Bug: 112657134
Test: Treehugger
Change-Id: I0dcd01bdad7d9c37294cd8b87eda54b4ac9d0a0b
Merged-In: I0dcd01bdad7d9c37294cd8b87eda54b4ac9d0a0b
(cherry picked from commit 9f93a12e)