telephony: Add support for choosing a default APN

 * Sometimes, the standard method of choosing the "first" available APN
   is not what we want. Consider the case where a certain provider has
   both a "normal" APN and an LTE APN. The LTE APN is what we want, but
   it's not chosen.
 * Add a new overlayable value "config_preferred_apn" to handle this. A
   device can override this. The format is "apn,mcc,mnc".

Change-Id: Ia6ca4159491bee15b3f18ad7ad524b8b0ffce2f2
TelephonyProvider: Handle database upgrade for MSIM

* need to add a boolean field 'preferred' to the carrier table in telephony.db

Change-Id: I9cf2c5bcebd7e7c3aca90f7e2a246b9d85d01c76