ros: mavlink dummy node: handle position target local ned mavlink messages and forward them to position_setpoint_triplet

ros: mavlink dummy node: listen to vehicle local position and publish to mavlink (LOCAL_POSITION_NED)

Replace offboard control setpoint topic with simple offboard control mode topic, remove setpoint data from topic

Added offboard actuator controls flags to offboard control mode and vehicle control mode to disable controls in att_control apps

if attitude/rates haven been used previously do not set the ignore flags
even if the message asks us to do so to keep the controllers running

Replace offboard_control_setpoint with offboard_control_mode
Remove all setpoint data from the topic as it's  not used anymore
(setpoint data is directly routed into position/attitude setpoint topics
for some time now)
Remove mode enum and replace with ignore booleans which map better to
the mavlink message
Mavlink: Rework parsing of offboard setpoints
Commander: in offboard mode set control flags based on ignore flags
instead of enum

Fixing small issues at ekf_att_pos_estimator

modified default pwm values and added comments to the startup scripts