SplitView: bugfix hiding splitter for last item

Change-Id: I8953d7fa4f1a1a940029270d4cb8f3d69da07bf7
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
SplitView: Always layout as if fillWidthItem is visible

Hiding the fillWidth item in the splitter is allowed, but
causes strange drawing/layout artifacts that can be
difficult to understand since the layout engine would ignore
all hidden items. This patch changes the implementation
by adding an exception to the rule. The layout engine
now treats the fillWidth item as if it is always visible.
Then, hiding it would just reveal a white field where the
fillItem would otherwise be, but the layout would otherwise
look correct.

Change-Id: I95ec51b595109e8f1efdc231c9a6697ee60aa483
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
SplitView: bugfix animating split items

Only assign a new width/height to a splitter item when
needed (that is, the value was clamped). Otherwise we just
end up breaking bindings and animations without a good reason.

Change-Id: Ic33007713f6450d52c9f5bd958fca74095413638
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>