Use unsolicited new message notifications instead of SIM storage

[JamesMarcogliese]

http://stackoverflow.com/questions/29257924/how-to-disable-gsm-modem-unsolicited-sms-arrival-message

[shgaurav]

If we can implement this, this will definitely decrease latency while checking and sending messages. The only issue would be hardware, however we have a shield which is directly connected thus connection issues are less likely to occur.

[JamesMarcogliese]

Would also reduce wear on the SIM