Displaying Spline Paths during flight

#### Issue details
When planning a mission using Spline Waypoints they are drawn with splines between them in the Flight Planner which is great.

Unfortunately when using the Flight Data screen for the actual flight they are drawn with straight lines between them. It can be a little disconcerting when the aircraft does a big arc between two way points rather than tracking directly between them, or vice versa.

It would be great if the curved planned path between Spline Waypoints could be correctly displayed in the Flight Data screen.

Thank you

#### Version
1.3.50.0 but probably all

#### Platform
[ ] All
[ ] AntennaTracker
[ X ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

Definitely Copter but presumably all.

Compare how spline waypoint paths are rendered in the Flight Planner with the straight-line rendering in the Flight Data screen. Trace the shared mission-path display entry points, then verify that Flight Data shows the same curved planned path between Spline Waypoints for Copter missions.

Written by the indexing model from the issue text.