Re-color one-way tiles to match their tileset

One-ways have always had this problem where they're always yellow. That
means unless you specifically use yellow, it'll never match the tileset.

The best way to fix this without requiring new graphics or changing
existing ones is to simply re-tint the one-way with the given color of
the room. That way, the black part of the tile is still black, but the
yellow is now some other color.

desktop_version/src/editor.h

@@ -239,6 +239,9 @@ class editorclass{
   int dmtile;
   int dmtileeditor;
 
+  Uint32 getonewaycol(const int rx, const int ry);
+  Uint32 getonewaycol();
+
   int returneditoralpha;
   int oldreturneditoralpha;