Tweens components simplification

I added to ashley the posibility to combine components. So, when a component is added, if a component of the same class is present, it tries to combine both, instead of removing the old one and adding the new one.
This PR take advantage of this, and remove the Tweens model component, which it was merely a grouper, and makes each basetween a component. This simplifies the model a bit. (If you are OK with this approach, we probably want to the same for behaviors).

It keeps TweensComponent the same, although now it can combine.