Create gsm_integration_code_update

Not sure if I'm following protocol here properly, Alex. This is an updated version of the main INO file. Main changes are:

-removed program control of the modem Rx pin (pin 3), which was hanging program flow
-simplified the display functions, saving a lot of calculation (numbers are assigned to specific digits on the seven-segment only once, instead of each time they are flashed for POV)
-correctly implemented the bit shift logic to allow easy swapout of common anode and cathode 
-put in a note on how to identify if a seven-segment display is common cathode or common anode
Merge pull request #9 from iamchriskelley/patch-1

Create gsm_integration_code_update