break out OTP library from auth.c into otp.c/otp.h   no functionality change at this point, but supports other apps ( like APM) using the OTP now.
Merge branch 'auth' of https://github.com/PX4/Firmware into auth

Conflicts:
	src/systemcmds/auth/auth.c
Merge pull request #352 from davidbuzz/auth

break out OTP library from auth.c into otp.c/otp.h