Ims: Fix the NullPointerException in getCountryIso() function

Added Null check for detector.detectCountry(), if this function call
fails, then CountryIso will be picked up based on the Locale.
CRs-Fixed: 490472

Change-Id: Ia94891629cf6170a821f76a718d4b965ae7ab802
Telephony(DSDS): MMS Auto Download.

Add MMS_TRANSACTION property which enables silent or prompt
modes to download MMS on non-DDS sub.

Change-Id: I52fe5c095e0d69c2e0d4a7fd5bfeb77bf3289380
Telephony: Change Default subscription property name.

Change default subscription property name from
persist.default.subscription to persist.radio.default.sub so
that it can be set by radio group access processes.

Change-Id: I0a75eca8c88c54e8f68ebd029abecb17249a546a