I think it's a good time to do some refactoring. I think that `focusFirst` method and the helper `_focusNext` and `_doFocus` should be extracted to some utility class (`aria.utils.Focus` ? or sth like that). They don't seem to fit into the `NavigationManager` IMO.

`PopupManager`, `Dialog` and `TemplateCtxt` all depend on `NavigationManager` only to use the call to `focusFirst`.

What do you think?