This patch makes the system map much better looking and easier to use.

0.846 change list:

* changed sprites on system map to animating models with effects (much prettier)
* now draw background of that system on the system map if it is loaded (if not draws current player level background)
* planets now show clouds and rings on the system map
* now unexplored part of the map (on system map and minimap) is a texture instead of a flat color
* added background on names on system/sector maps
* now effects handle scaling better
* changed black hole description to "usually don't have planets"
* made lines on sector map thinner
* fixed a filename issue in TextureCtx::load
* moved MapLevelMaxZoom to database instead of hardcoded
* turned off some shadow mapping stuff that was still doing stuff (doesn't seem to have any real fps impact though)
* fixed depth buffer clear between SORT_TYPE_TRANSPARENT_BACKGROUND and SORT_TYPE_OPAQUE_BACKGROUND2 to be more robust