Igcs 136 ardrone ftp

** NOT READY TO BE MERGED YET* 

Opening PR so @cnatoli and @andymoe  can follow along and provide feedback if asked.
For each of the AR.Drone AT command methods you have below please turn requestStr (Also it should be requestString btw) into extern constants as follows:

At the bottom of the header file after @end:
`extern NSString * const ARDroneATCalibrateMagnetometer;`
...
...

At the top of the method file after the imports:
`NSString * const ARDroneATCalibrateMagnetometer = @"AT*CALIB=1,0\r";`
...
...

This will allow us to use these in other classes for instance in an interface that talks over UDP and separately in an interface that uses the FWR.