Enable full support for SMS Cell Broadcast.

Implement full support for SMS Cell Broadcast (3GPP TS 23.041).
Includes support for ETWS and CMAS emergency message types.
Includes GSM and UMTS support (CDMA will be added later).

Note: the change to GsmAlphabet.java is only necessary if the
SMS national languages support patch has been applied. If that
change has not been applied, then the changes to GsmAlphabet.java
in this patch set can safely be ignored.

Change-Id: Ia0362c53695b8ef9a0982f558f1cffa912def34b