Planned / implemented layout widgets

[Girildo]

Hi @vanifatovvlad
Here to report the widgets that I have either already implemented or I plan to implement:

• ScrollList (bidirectional and virtualized) -- as discussed I have to think whether it makes sense to improve the ViewportSize to be treated as constraint.
• PaddingBox
• ConstrainedBox (For widget that are forced to stay withing given constraints, especially for min sizes)
• UnimobButton

Some further widgets that I think would be useful/I could see implementing in the near future are

• AspectRatio