Fixed Infinite map zoom

We set the PlanetariumCamera to the selected vessel and after this we removed this new "entry" from the PlanetariumCamera.fetch.targets list. (FocusFragment.cs:45) If you switched back to the map view the PlanetariumCamera is set to a vessel that doesn't exists on the PlanetariumCamera.fetch.targets list anymore.

This will fix #188
Ok, let's do that for now. At some point we should really remove state buttons in favor of single-action buttons. The current behavior is very unintuitive (e.g., @Gaiiden's comments on #162).