Some improvements for FlxObject

- removed cachedGraphics, region and framesData and pixelPerfectRender - FlxObject should not have graphical data. They are now introduced in FlxSprite and FlxTilemap.
- moved static functions and variables to the top
- made debugBoundingBoxColor a Null<Int>, making _boundingBoxColorOverritten obsolete (null means: use the default colors)