Performance optimizations and aspect ratio

• many, many performance optimizations. Things are calculated only when there is a need.
• keepAspectRatio added

Animation system

Animation system added:

obj.yoga.animationConfig  = {
    time: 250,
    easing: t => t
}

Fixed `position: absolute` bug

Fixed bug with position: absolute elements positioned using bottom/left properties

PIXI5 support

Added support for PIXI5