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
> You need to have 100% to all parents? What is new to this PR compare to issue discussion?

More exaclty you need to have a size in either percentage (100% or other value) or in px (or other unit), if I understood well. 

What is new for me is that I realize only now that this (apparently) forbids getting the natural height - while I initially only perceived the constraint in the sense that the user must not forget setting sizes.

This is the annoying thing in general. My more specific pain is related with the way delite's HasDropDown/popup deal with sizing of the dropdown/popup. In practice, the PR produces regressions for the List used inside the popup, with or without embedding it in LinearLayout. This case is trickier, because delite/popup needs to measure the height before deciding to set the height to a lower value (depending on the available space).
Anyway, that are my concerns.