Make sure sprite colors in the editor don't update more than 30 FPS

This adds Graphics::crewcolourreal(), which is like the
entityclass::crewcolour() that the editor already uses, except for the
real color instead of the color ID. Also, editorclass now has an
attribute `entcolreal` so enemy colors don't update more than 30 frames
a second.

desktop_version/src/editor.h

@@ -6,6 +6,7 @@
 #include <vector>
 #include <string>
 #include "Script.h"
+#include "Graphics.h"
 
 class edentities{
 public:
@@ -150,6 +151,7 @@ class editorclass{
   int getlevelcol(int t);
   int getenemycol(int t);
   int entcol;
+  Uint32 entcolreal;
 
   //Colouring stuff
   int getwarpbackground(int rx, int ry);