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
I wouldn't come back to this if I wouldn't face troubles with this PR for the use of List in ComboBox. 
I still wonder whether the systematic embedding of List inside LinearLayout doesn't just hide a behavior change of List, due to the styling changes in this PR which might be annoying in some contexts such as mine - but not only in my case.

So, how do you get (after the styling changes in this PR) a List having its *natural* size (width and/or height)? Say, a list with only a few elements, which does not need scrolling - which sounds as quite a generic use-case. Before the PR, just using the List as-is, without any custom style, it used to get its natural height. Now, it gets the 100% setting (due to the change in d-list class), so if the page contains the list plus a small line of text, you get scrollbars on the page, which are annoying because normally not necessary. 

Even if you try to override List's height: 100% in the app with height: auto, it still doesn't give the natural height, it gives a zero height. This seems to be related with this PR's replacement of position: relative by position: absolute in d-list-container class. 

@dmandrioli, what would be your take about how to get a List with natural height?