Add my scene view icons

Add my scene view icons: status overview icons, element toggle icons, parts from which they're assembled and the SVG master.

The icons to be used in the editor are located in files/opencs/, everything else is the source files for those icons so you can recreate them from the SVG master e.g. after editing it.

The scene view status icons are named as a bitfield, according to Zini's request: scene-view-status-X.png where X is a sum of all the digits for the elements used. 1 for references, 2 for pathgrid, 4 for water, 8 for fog and 16 for terrain.