GCS Control: Make SDL optional

To compile with SDL joystick input support compile GCS with
make GCS_QMAKE_OPTS="CONFIG+=SDL" -j7 gcs
GCS Control: Remove commented code
Fix for excluding SDL
GCS Controller: Add an option to control via GCS Receiver instead
GCS Control: Update the GCS Receiver object
GCS: Also exclude sdlgamepad library when unused
SDL: Mask out more includes
SDL: Only copy the dll when used
GCS: Fix typo for optional SDL
Merge branch 'next' into gcs_control
Fix flickering and improve antialiasing.
Fixed PFD telemetry arrow loading.
math: include the API declaration to ensure implementation matches
ut: add unit tests for misc_math.c functions
FlashFS: fix formatting with multiple instances

The old format command took a (0) in for no reason which
because the uintptr_t to the file system and obviously
results in an error erasing flash.
unit test: add license headers and pointers to google test docs
Merge pull request #474 from peabody124/flashfs_format_fix

FlashFS: fix formatting with multiple instances
ut misc_math: allow +180 or -180 as valid and correct for 180deg errors
ut misc_math: test a much larger multiple of 360deg around +/-180
ut misc_math: remove disabled reversed min/max test