Cleanup duplicated magic numbers in joystick code

LinkInterface and Vehicle uses mutexes to synchronize writing bytes to the link instead of queued signals

Cherry pick joystick fixes from stable and fixup merge

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Add support for multi-press joystick buttons

This commit adds the emergency stop as button action to the joystick.
Enables a user to map emergency stop to a button of the joystick.

Fix cmake build in macOS
Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Allow plugin to add flight modes to joystick button actions

Support up to 64 buttons, not limit to 16
Send a single button command and not a stream of commands at 25Hz
Send button commands through signals (it's coming from a different thread)
Hide gimbal support through analog channels (there are no MAVLink messages to handle it)

Map gimbal controls
Keep track of gimbal position within Vehicle

Add gimbal to external control signal

Add camera trigger
Add video start/stop/toggle recording
Add gimbal pitch and yaw

Fix debug output

When starting up, if you start the GS before connecting the bluetooth joystick the QGC needs to be closed and restarted to get it to recognize the joystick

Default to ThrottleModeDownZero

When starting up, if you start the GS before connecting the bluetooth joystick the QGC needs to be closed and restarted to get it to recognize the joystick

Add note about button bits

This reverts commit c01ceadd.