Fixed a bug where a rearrange was not always done

This happened only when the size of the layout didn't change.

Task-number: QTBUG-31570

Change-Id: Ia090c0062fa8fc3eb6f648592529ee8fcd025593
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Improve the Styles page and add missing SliderStyle property

- I noticed we incorrectly exposed sliderPosition.

- This adds some more custom style examples for the gallery and
makes the second column actually different from the first.

Change-Id: I73f0d613f51f6e75aaf734fd4e4c9fdb890e3e42
Reviewed-by: Caroline Chao <caroline.chao@digia.com>