Rover: cleanup mavlink_system setup
Plane: cleanup mavlink_system setup
AP_TECS: remove lag from height demand in landing

this predicts ahead the height demand for landing, where we have a
continuous demanded descent. This removes the effect of the lag
introduced by the height demand filters
AP_NavEKF: Do not reset vertical velocity state from GPS

Doing this can cause large height and height rate errors if large GPS velocity errors cause the GPS tn be rejected for long enough to cause a timeout and reset of states.
AP_NavEKF: Use named states for velocity reset

Readibility improvement
Copter: Fix LAND overshoot issue
Copter: minor formatting fixes
Mission: allow 15 do-jump commands on Pixhawk
AP_NavEKF: Improve robustness to long periods without GPS