CardsListView: Make sure it never will have horizontal scrolling
When a ListView has rightMargin and/or leftMargin and Flickable has "automatic" contentWidth (ie wasn't overridden) Flickable will consider as content width the whole flickable width plus right and left margins, causing an unwanted horizontal scroll.
override contentWidth in CardsListView in order to always be the listview width minus the margins, which will cause in the end always wide exactly as the listview which is exactly what's needed in the CardsListView case