Improvements to the Navigator

[mlewlp]

The new Navigator feature (switching pages/templates without having to leave Oxygen) is incredibly welcome and useful. It really helps maintain a good "flow state" as opposed to going in and out of the editor repeatedly. Thank you very much for this feature!

With that said, I feel like it has a couple of rough edges, in the sense that it will happily allow you to open items in Oxygen that aren't meant to be opened there. The two examples I've found so far (and possibly the only ones) are that you can open pages or posts that have Gutenberg content, or that are being rendered by another template that doesn't have an Inner Content element.

I would submit that both of those conditions should be checked before allowing the user to switch to a different item. If Gutenberg content is present, then probably the page shouldn't be editable "accidentally" in Oxygen. And opening a page in Oxygen that is rendered by a template without Inner Content is just plain weird. Maybe just add an "Are you sure?" confirmation before allowing the switch in those cases.

Also, it would be great to have a feature where custom post types could be opened via the Navigator. But I feel that would require an admin setting, similar to (but in addition to) the current Post Type Manager under the Client Control settings.