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
SDL: make the default NO_SDL

This is in order to not change the default behavior with
not including SDL.

to compile without SDL
make GCS_QMAKE_OPTS="CONFIG+=NO_SDL" -j7 gcs
Merge pull request #397 from peabody124/gcs_control

GCS Control via GCSReceiver