Centralize NPOT support check for image, export it to isSupported

src/modules/graphics/opengl/Image.h

@@ -37,7 +37,6 @@ namespace graphics
 {
 namespace opengl
 {
-
 	/**
 	* A drawable image based on OpenGL-textures. This class takes ImageData
 	* objects and create textures on the GPU for fast drawing.
@@ -138,6 +137,8 @@ namespace opengl
 		bool loadVolatile();
 		void unloadVolatile();
 
+		static bool hasNpot();
+
 	private:
 
 		void drawv(const Matrix & t, const vertex * v) const;