Added code to support Cell Eng Data and also to suppress Unsolicited SMS Notifications

[kcuhc255]

The changes are clearly delineated by comments in both the .cpp and .h files.

To suppress the Unsolicited SMS notifications:
fona.setURCMode(false); // Suppress Unsolicited Messages

The following call returns the LAC, CID, MNC and MMC:
fona.getCELLLoc(0, dataBuffer, sizeof(dataBuffer));

This is the code I added to the Example sketch to test the engineering data capture. You need to add a "Q" item to the menu. :

/*****************************************/
case 'Q': {
  char celldata[220];
  // getCELLLoc(uint16_t *errorcode, char *buff, uint16_t maxlen)
  fona.getCELLLoc(0, celldata, 220);
  Serial.print("Got cell data"); Serial.println(celldata);
  break;
}

// NOTE: The following is superfluous because I call the endCELLLoc() within the call to acquire the data in order to avoid flaky behavior.
case 'Z': {
// endCELLLoc(uint16_t *errorcode)
fona.endCELLLoc(0);
Serial.println("Ended acquiring cell data");
break;
}