Adding 1/n step(s) for routing

[Kimaidou]

At present, Navit only find the route from one position to one destination. I think it would be usefull to have the possibility to add one (or more) steps. For example, I wan't to force the route to pass along this fuel station. So basically, we set the position A (or set by gps), then the destination B --> the route is calculated and showed. Then I can click on the map, or select a poi or bookmark and say "choose as a step" C --> the route is re-calculated from A to C, then from C to B

I think it would be a great improvement.

[KaZeR]

Duplicate of #46