Ship trajectory shown in system view. Dynamic body returns Orbit trajectory, hyperbolic trajectories made possible.

In this PR, I implement following features:
* Each dynamic body now can return correct struct Orbit calculated from its initial velocity and position. It can be both ellipse or hyperbola.
* Orbit of player ship and its position at given time are shown in the F6-system map.

Now, it needs some testing, because there is a lot of equations involved and although it seems to be working well, there can still be some bugs present. 

This probably partly solves #1648, #146 and #985, it might be useful also to #1633 once the apoapsis and periapsis are exposed to Lua and to #1745.