v2.2.1: Update changelog, demo, and core for Version 2.2.0

- Added `Version 2.2.0` section to `changelog.md` with feature, improvement, and bugfix notes.
- Introduced a "4day" view with navigation, rendering, and localization support.
- Enhanced drag-and-drop logic to fix disappearing and unresponsive appointments.
- Updated demo with "4day" view buttons, shadow fixes, and language select improvements.
- Refreshed documentation with new features, updates, and bug fixes for `Version 2.2.0`.