Separate itemSize into height and width

[jlnrrg]

After looking through the code I noticed that itemSized is applied to both width and height.
This is great for the use of Icons, as they are a square (at least most of the times in my understanding), but leads to issues with custom widgets.

Lets say I use a custom widget as an icon (see #54), then there is a space build, which I can not get rid off:
(notice the top and bottom space)

here it would be great imo to either have a width and height property or let the user pass a size class.

Furthermore, but this could be another issue, if no size is passed the widget should autosize based on its children.

[ariefwijaya]

Any update on this?