"toggle()" method usable outside and visible parameter for the main toggler icon

[regisandre]

Hello,

1. I made the toggle method usable outside the main "toggler" icon. For example, now we can use the toggle() method on any screen button or in an onPressed parameter of an Icon in an app bar.
2. I add a visible parameter for the main toggle icon to hide it if we use the toggle method outside the main "toggler".
3. I add an example of the new "toggler" in the main.dart example.
4. SideNavigationBarItem is now a custom Material widget because the ListTile caused a faded widget color.

[jksevend]

Hey @regisandre
Thanks for the effort! Will have a look at it once I have some time left.

[jksevend]

Use debugPrint() from material here please