- landing_gear: refactor state name
- Add the keep state to the landing gear message
- Adapt FlightTaskManual, FlightTaskAutoMapper, mc_pos_control,
to review message definition

FlightTaskAutoLine: ensure that desired speed along track does not exceed maximum speed at threshold to target

Also update some comments.

In case we activate the task and don't have a locked yaw, we should
initialize the yaw setpoint with NAN to avoid any abrupt changes.

- better in terms of dependencies:
  - the position controller code depended on position topics for yaw
  - mc_pos_control does not have to be run for Stabilized mode
- the code path is much simpler, and thus less error prone. This is
  especially important since Stabilized is often used as a fail-safe flight
  mode.

- move the update after the integration: a new computed jerk has an impact at the next epoch only
- add jerk reduction in case of too large integration time: when a jerk of "min_jerk" during dt is too much
- add jerk reduction if the integration time is larger than the predicted one and that integrating that jerk would lead to an acceleration overshoot
- rename some variables

Trajectory - Add time synchronization between trajectories. Split update(...) function into updateDurations(...) and integrate(...) to be able to insert time synchronization in between.

Derivation by Mathieu Bresciani:
https://github.com/Auterion/trajectory_generator

* Add attitude sub to mc_pos_control for yaw usage.

* Initialize pos control _states struct.

* Remove unnecessary init for struct in mc pos ctrl.

* Only use att topic for yaw setting in FlightTask.

Signed-off-by: Roman <bapstroman@gmail.com>

Signed-off-by: Roman <bapstroman@gmail.com>