[Parent-Issue] Rework tweening system

[stringdotjar]

The tweening system, although has a solid foundation, is currently unfinished. The FlixelTweenManager class should have more methods for having better control of the active tweens it's in charge of. It should also be refactored to ensure consistency with the familiar HaxeFlixel library.

Sources:
https://api.haxeflixel.com/flixel/tweens/FlxTweenManager.html