Add Graphics.Element.scrollContainer

[avh4]

This is a proposal to add the capability to create scrolling regions in UIs built using the Graphics.Element API.

With this change, here is how you would make a 200x300 region containing a vertically-scrolling block of text:

main = plainText "my text..." |> width 200 |> scrollContainer 200 300 

Graphics.Element.scrollContainer as proposed here can also be used to make viewports that scroll horizontally or that scroll both vertically and horizontally.

As far as I know, there is currently no way to achieve this type of effect with the core API.

[evancz]

I guess we'd just do it in HTML these days.

[evancz]

I guess we'd just do it in HTML these days.