Correct initial/minimum size of default QML ColorDialog

Change-Id: Idd53d9c7246b17a9159faec06a7ce6c6355cd09f
Task-number: QTBUG-32572
Reviewed-by: Liang Qi <liang.qi@digia.com>
Keep the QML ColorDialog's controls in sync with the color property

Until now, the user could change the color by dragging the crosshairs
or the sliders, but if the application set the color property, it did
not programmatically move the crosshairs and sliders.

Task-number: QTBUG-32545
Change-Id: Idd54e711400dfd78d570161297559f9521c1d67f
Reviewed-by: Liang Qi <liang.qi@digia.com>