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
AP_NavEKF: Reduce time required to recover from GPS timeouts

The time required for GPS to be lost or rejected before vehicles with airspeed sensors either reset to GPS or invoke the zero side-slip assumption to constrain drift has been reduced from 15 to 10 seconds
A duplicate zeroing of the GPS position offset has been removed
If the vehicle is a non hovering vehicle (eg a plane) then the speed at which the GPS offset is pulled back to zero after a reset is increased from 1 to 3  m/s

This also improves recovery from bad inertial data for planes
AC_PosControl: change keep_xy_I_terms to a parameter of init_xy_controller
AC_WPNav: provide reset_I to init_xy_controller
AC_PosControl: remove various unnecessary timing hacks
AC_WPNav: remove various timing hacks