Install some styles only for Qt 5.2 or better

New styles such as BusyIndicatorStyle and SwitchStyle are only suitable
for Qt 5.2 or better.
Add a SrollViewStyle for Qt 5.2 or better

Qt 5.2 introduced the transientScrollBars property that we always set
to true. Maybe in the future we can detect whether the main input
device is a mouse or touch and set this property to true only for touch.
Fix imports for some styles
Update qmldir