Limit width of launchpad window

Without limiting the size of the launchpad window, the application
prepares itself for the worst case, taking the screen size as maximum
size to allocate its pixel buffers. Limiting the maximum width to a
reasonable value reduces the memory footprint.

demo/src/app/launchpad/main.cc

@@ -165,7 +165,7 @@ int main(int argc, char **argv)
 	long initial_h = read_int_attr_from_config("height", 400);
 
 	/* init platform */
-	static Platform pf(initial_x, initial_y, initial_w, initial_h);
+	static Platform pf(initial_x, initial_y, initial_w, initial_h, 400);
 
 	/* init canvas */
 	static Chunky_canvas<Pixel_rgb565> canvas;