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

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.

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

Default to ThrottleModeDownZero

Add note about button bits

This reverts commit c01ceadd.

Don't send button pressed bits to MANUAL_CONTROL

Remove deprecated button count testing

Remove the concept of reserved buttons for manual control

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

Some digital joysticks have already this correction
Add habilit to add or removecircle correction
Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Joystick axes and buttons can now be monitored even when the
joystick input is disabled.

Revert "Removed code that cut off the last 25% of joystick motion in either direction. I'm not sure what the original purpose of this code was."

This reverts commit 4c34fb38.

Changed Joystick._exponential from bool to float. It can now be set between 0 and -0.5 by user using a slider.