Began stripping down the Universe Editor clone to make a Map Editor.

Usage :
- Click on a system toggles it from the selection,
- Button "Save Map" saves the selection to saved_map.xml.

WARNING : still very partial WIP status !!!
- Lots of features still not functional or not even present,
- Some buttons redirected, but still not properly wired in,
- Lost view mouse-dragging, have to reintroduce it,
- And probably some other bugs and glitches I still have to find...