RibbonBar / ButtonSelection In SplitButton

Two new properties have been introduced for RibbonBarSplitButton - EnableButtonSelection and SelectedButtonIndex.

EnableButtonSelection allows buttons inside the drop-down to be selected as default, once they are clicked. In the example you can select a Hat for instance, and this will trigger several actions - update the image with the selected "hat", update the text with the name of the selected hat and, last but not least, update the default action of the split button.

SelectedButtonIndex on the other hand can be used, both, to select a button statically (without the option of selecting another through a click in the drop-down) and in combination with EnableButtonSelection=True, when it can be used to monitor the selection for example, or to alter the default logic of EnableButtonSelection=True.

One important thing to mention about this new feature of RibbonBarSplitButton is the logic in which the image and text are updated:

- The text of the split button is updated only if it's not set (splitButton.Text=...) - then text is gathered from selected button;

- The Image is updated as follows - if there is an applicable image set directly to the splitButton (splitButton.ImageUrl = ... or splitButton.DisabledImageUrlLarge etc.) - it's applied. If there is no such image -> the split button will try to apply an image from the SelectedButton. If there still isn't an image to apply -> default image is applied.