Custom builders for animations

[muezz]

This PR adds custom builders and props for the following animations:

• Animation of the child, before the pie menu opens: Currently, bouncing animation is the default. This allows you to disable it completely or pass a custom transformation.
• Animation of the pie menu itself: This allows you to pass the curves and the duration.
• Animation of the child while the pie menu is open: This allows the user to set up an animation of the child widget while the menu is open sort of like the tilt animation in pinterest.

[muezz]

@rasitayaz Could you point me to the right place where the children widgets are built and rendered below the overlay layer? If you check the example of the ListView page, the animation shows an opaque child below it. I need to apply the animation to that too.

If you are able to take over and finish this, let me know.