v2.1.0: Span groups, new precise position entry tool, OS span mode control

New features:

• Span groups: span wallpapers on groups of displays.
• New tool to set the physical display positions for advanced span. Enables accurate fine tuning of dragged positions.
• Control system wallpaper span setting. No more need to check the setting in the system settings.

Fixes and enhancements:

• General:

  • Fix out of order wallpaper changes when user and slideshow acted concurrently
  • Support capitalized file extensions
  • Default locale is now system locale

• Linux:

  • PopOS support
  • Ubuntu Studio support

• Windows:

  • Uninstaller now asks whether to uninstall settings and profiles