Fix #270: on iOS, List doesn't scroll correctly when it is inside a deli...

Set position:absolute, width:100% and height:100% on List's inner node => The List is no longer sized by its children
Set width:100% and height:100% as default on List => The List's parent height must be defined, see List.md
With and without the changes in this PR, the content is lengthier than the page, and the user can scroll. It's not exactly the same scroll (List's scroll vs. page scroll), but it looks close. Both are possible, it's just a question that may hold whether we want all List samples/test to use LinearLayout.

That said, there's an additional problem: in FF, with this PR at least samples/list/customCategoryRenderer.html gets a double scrollbar if the window is smaller than the content - which is a regression (no double scrollbar without these changes).