Changelog:
- New widget: ContextMenu
- Added handleWindowEvents function to SFML backend (only for SFML 3)
- Added onRightClick signal to ListBox
- Added onTabRightClick signal to Tabs
- Added setSmooth and isSmooth to CanvasSFML
- Changed the way the view is handled in CanvasSFML
- Pressing escape now closes the menu from ContextMenu or MenuBar