Hacked in changes for SONAR on PIXHAWK

-Will enable sonar to work correctly on pin 15 (middle pin of 6.6 ADC
plug).
-Will send mavlink sonar distance and voltage to GCS
-Will display Raw value, Distance, and voltage in TEST/SONAR CLI mode.
-Tested with Mission planner, CLI Mode, and datalogs.

*Probably will not scale properly on pins 13 and 14 because pin 15 is on
x2 voltage divider that scales to 3.3V
*Probably will not work on APM 2.x with out adding in #DEFINE functions.
*NOT TESTED IN FLIGHT AS OF YET.