FlxDebugger no longer extends flash.display.Sprite.

Even though the debugger has several overlays (console window, watch windows, etc), it makes no sense to me that it extends flash.display.Sprite. I've created an "overlays" property in the debugger and attached all overlays there.

It will make the FlxDebugger API much simpler because all the inherited flash.display.Sprite methods will be gone.

From now on, plugins and developers can use FlxG.debugger.overlays.addChild() to add their own debug overlays.