Fixes wind_comp, brake pitch timer, thr. peaks

There was an error in the velocity axis used to update
brake_timeout_pitch (vel_right instead of vel_fw)

The wind_comp was not enough filtered for the Pixhawk (400Hz), so I
added a specific time constant (TC_WIND_COMP) to have the expected
filter with 400Hz controllers.

About throttle peaks, after some tests and from logs, they happen when
hybrid switches to loiter.
There is always a difference between Alt and DesiredAlt (DAlt), but,
when loiter engages, it initializes DAlt = Alt and the copter tries
immediatelly to reach that new setpoint. So the solution would be to
init_loiter_target() just as it was in pre-onion code : only x/y and not
z. and to be able to pass parameters like that
wp_nav.init_loiter_target(inertial_nav.get_position(), Vector3f(0,0,0));

Well, from this new code structure, it seems not possible with current
functions so I've used set_loiter_target that init position passed as
parameter and velocity to 0 (as expected).
BTW, I think there was something wrong with set_loiter_target function,
the "Vector3f& position" parameter was not used at all...
I moved the reset flag from init_loiter_target to set_loiter_target.

This new code has not been tested for the moment, I hope it will fix the
throttle peaks.

Randy, for sure there is something easier to do but before we could give
a try to check if this fixes the bug completely.