[Qt-qml] Advanced layout support

[Adriano Rezende]

Well there is a 5th approach which is to use LayoutItem wrappers.

RowLayout {
    LayoutItem {
        minimumWidth: 200
        Item {}
    }
}

* Advantages
- More explicit API (but also more confusing. Which elements require
LayoutItem?)

* Disadvantages
- Code bloat
- Each element should be wrapped by a LayoutItem (not a clean path)
- Make it hard to add items dynamically (always need to wrap the item
before inserting)

Br,
Adriano