Fix property naming for OptionSelector/ItemSelector

[Tim Peeters]

OptionSelector and ItemSelector have these two properties:

    /*!
      \preliminary
      Specifies whether the list is always expanded.
     */
    property bool expanded: false

    /*!
      \qmlproperty bool expanded
      Is our list currently expanded?
     */
    readonly property alias currentlyExpanded: listContainer.currentlyExpanded

The name "expanded" is not clear, "alwaysExpanded" would be better. "currentlyExpanded" should be named "expanded" (we don't use the currently- prefix anywhere else).

I propose to rename "expanded" to "alwaysExpanded" (keep expanded as deprecated for a while), and once the old deprecated "expanded" has been removed, "currentlyExpanded" can be deprecated in favor of a new "expanded".