Sub should move away from using firmware-side button press handling

[Williangalvani]

Sub has a lot of functions that are triggered from buttons handled on the firmware side. That is not how most of the vehicles work, and it makes it harder to control it via MAVLink for autonomous functionality, and also requires specific handling on the GCS.
I'm opening this issue to document what can easily be changed and what needs further work.

Here's an idea of how to map things:

Button function	MAVLink function
k_none	N/A
k_shift	N/A
k_arm_toggle	MAV_CMD_COMPONENT_ARM_DISARM
k_arm	MAV_CMD_COMPONENT_ARM_DISARM
k_disarm	MAV_CMD_COMPONENT_ARM_DISARM
k_mode_manual	MAV_CMD_DO_SET_MODE
k_mode_stabilize	MAV_CMD_DO_SET_MODE
k_mode_depth_hold	MAV_CMD_DO_SET_MODE
k_mode_poshold	MAV_CMD_DO_SET_MODE
k_mode_auto	MAV_CMD_DO_SET_MODE
k_mode_circle	MAV_CMD_DO_SET_MODE
k_mode_guided	MAV_CMD_DO_SET_MODE
k_mode_acro	MAV_CMD_DO_SET_MODE
k_mode_surftrak	MAV_CMD_DO_SET_MODE
k_mount_center	GIMBAL_MANAGER_SET_PITCHYAW
k_mount_tilt_up	GIMBAL_MANAGER_SET_PITCHYAW
k_mount_tilt_down	GIMBAL_MANAGER_SET_PITCHYAW
k_camera_trigger	DO_AUX_FUNCTION
k_camera_source_toggle
k_mount_pan_right	GIMBAL_MANAGER_SET_PITCHYAW
k_mount_pan_left	GIMBAL_MANAGER_SET_PITCHYAW
k_lights1_cycle	new AUX_FUNCTION
k_lights1_brighter	new AUX_FUNCTION
k_lights1_dimmer	new AUX_FUNCTION
k_lights2_cycle	new AUX_FUNCTION
k_lights2_brighter	new AUX_FUNCTION
k_lights2_dimmer	new AUX_FUNCTION
k_gain_toggle	Handle on GCS?
k_gain_inc	Handle on GCS?
k_gain_dec	Handle on GCS?
k_trim_roll_inc	SET_ATTITUDE_TARGET
k_trim_roll_dec	SET_ATTITUDE_TARGET
k_trim_pitch_inc	SET_ATTITUDE_TARGET
k_trim_pitch_dec	SET_ATTITUDE_TARGET
k_input_hold_set	Handle on GCS
k_roll_pitch_toggle	Handle on GCS
k_relay_1_on	DO_SET_RELAY
k_relay_1_off	DO_SET_RELAY
k_relay_1_toggle	DO_SET_RELAY
k_relay_2_on	DO_SET_RELAY
k_relay_2_off	DO_SET_RELAY
k_relay_2_toggle	DO_SET_RELAY
k_relay_3_on	DO_SET_RELAY
k_relay_3_off	DO_SET_RELAY
k_relay_3_toggle	DO_SET_RELAY
k_servo_1_inc	DO_SET_ACTUATOR
k_servo_1_dec	DO_SET_ACTUATOR
k_servo_1_min	DO_SET_ACTUATOR
k_servo_1_max	DO_SET_ACTUATOR
k_servo_1_center	DO_SET_ACTUATOR
k_servo_2_inc	DO_SET_ACTUATOR
k_servo_2_dec	DO_SET_ACTUATOR
k_servo_2_min	DO_SET_ACTUATOR
k_servo_2_max	DO_SET_ACTUATOR
k_servo_2_center	DO_SET_ACTUATOR
k_servo_3_inc	DO_SET_ACTUATOR
k_servo_3_dec	DO_SET_ACTUATOR
k_servo_3_min	DO_SET_ACTUATOR
k_servo_3_max	DO_SET_ACTUATOR
k_servo_3_center	DO_SET_ACTUATOR
k_servo_1_min_momentary	DO_SET_ACTUATOR
k_servo_1_max_momentary	DO_SET_ACTUATOR
k_servo_1_min_toggle	DO_SET_ACTUATOR
k_servo_1_max_toggle	DO_SET_ACTUATOR
k_servo_2_min_momentary	DO_SET_ACTUATOR
k_servo_2_max_momentary	DO_SET_ACTUATOR
k_servo_2_min_toggle	DO_SET_ACTUATOR
k_servo_2_max_toggle	DO_SET_ACTUATOR
k_servo_3_min_momentary	DO_SET_ACTUATOR
k_servo_3_max_momentary	DO_SET_ACTUATOR
k_servo_3_min_toggle	DO_SET_ACTUATOR
k_servo_3_max_toggle	DO_SET_ACTUATOR
k_custom_1	N/A
k_custom_2	N/A
k_custom_3	N/A
k_custom_4	N/A
k_custom_5	N/A
k_custom_6	N/A
k_relay_4_on	DO_SET_RELAY
k_relay_4_off	DO_SET_RELAY
k_relay_4_toggle	DO_SET_RELAY
k_relay_1_momentary	DO_SET_RELAY
k_relay_2_momentary	DO_SET_RELAY
k_relay_3_momentary	DO_SET_RELAY
k_relay_4_momentary	DO_SET_RELAY
k_script_1
k_script_2
k_script_3
k_script_4