Changelog:
- Added uniform scrollbar access to all widgets with a scrollbar
- Added getter for hovered item to ListBox, ListView, PanelListBox, Tabs and TreeView
- Added option to buttons to only repond to clicks and ignore space/return key presses
- Added setItemIndexInParent and getItemIndexInParent functions to TreeView
- Added changeItemHierarchy to TreeView
- Scrollbar::setOrientation will no longer flip width and height
- Scrollbar::setSize no longer affects orientation once setOrientation is called
- Grid didn't update its size in remove and setAutoSize functions while auto-sizing
- Opacity of ScrollablePanel wasn't applied to its scrollbars
- Setting opacity of SeparatorLine had no effect
- SFML backend no longer uses sf::Keyboard::isKeyPressed to check modifier keys