- Enable is_pinned and is_archived handling in Rust and database
- Make sure sessions returned to QML are sorted by pinned first, timestamp second
- Mark message unarchived, when a new message arrives
- Use DelegateModel to implement "active" and "archived" splitting
- Session can self-request to switch groups
- MainPage.qml rewrite, basically
- Enable/add pinned/archived controls in QML
- Minor improvements here and there
Closes #219 (closed) and #220 (closed)