Added NavigationBar.MoveNavigationPaneDown and NavigationBar.MoveNavigationPaneUp which can be used to adjust the position of a NavigationPane.
(Use NavigationBar.CanMoveNavigationPaneDown and NavigationBar.CanMoveNavigationPaneUp to test if the corresponding method is valid).
Validated Microsoft .NET 5 compatibility.
Added NuGet packages for Microsoft .NET Core 3.1 variations of the assemblies.
Realigned API namespaces for clarity and consistency with other platforms.