Solar system browser update
Updates of the Solar system browser:
1) The "fictive system barycenter" is not displayed now (it is a barycenter used to add a catalog star with a custom data). This allows to add a catalog entry for the Sun with proper temperature and rotation axis/period.
2) Ability to show a barycenter of a binary planet and navigate it by the same manner as a barycenter of a binary star (new checkbox in the settings at the left).
3) When mouse is held over the table, navigation buttons appear on it ("enter satellites level" and "return back"). It is possible to display these buttons permanently in every table cell, but they may overlap the cell text (the back button on the screenshot already does that).