Added header file with common physical constants.
Updated library functions to use physical constants file.
Updated flight modules to use physical constants file.
Updated PiOS files to use physical constants file.
Updated GCS files to use physical constants file.
Added the shared API directory to simulator targets.
Fixes for header files, floating point trig functions, and incorrect
conversions.
Added shared/api to GCS include directory.
Fixed missing newline.
Resolved merge conflict.
Merge pull request #328 from kubark42/phys-constants

Group all physical constants into one file