New skin properties for Dialog widget

Adding the possibility to define new skin properties for the dialog title bar.
The properties added are:
- titleBackgroundColor
- titlePadding
- titleBorder
- titleBorderStyle
- titleBorderColor
- titleBorderRadius
I think it would be better to keep `borderTopRightRadius` and `borderTopLeftRadius` radius to 6, remove the `marginTop` and set the `paddingTop` to 33+12