WPNav: add spline support
Mission: minor comment update
Copter: integrate spline navigation
Copter: minor format change
AutoTest: add copters spline test
AC_WPNav: add get_spline_yaw
Copter: integrate get_spline_yaw
WPNav: add yaw control for straight line wp nav
Copter; integrate WPNAV's get_yaw
Copter: remove original_wp_bearing

To-Do: extend wpnav yaw control to only repoint nose towards waypoint if
it is more than 5m or 10m away
GCS_MAVLink: add MAV_CMD_NAV_SPLINE_WAYPOINT cmd

This is the same as a NAV_WAYPOINT except that the vehicle flies a
spline curved path to the destination
GCS_MAVLink: generate after adding NAV_SPLINE cmd
Mission: add decoding of NAV_SPLINE command
Copter: add do_spline_wp and verify_spline_wp functions
AutoTest: update copter_spline mission
Copter: remove spline handling from regular wp_nav