Private Communities: allow for the creation of a public page

When you make your community private, the only page that is visible for a non-logged in user is the login page. However this login page cannot be customized much; you can set a background and add a short text.

It would be handy to be able to customize this login page further or create a custom page that can be made public where we'd be able to customize it with banners, widgets and texts that would introduce non-logged in user to the community and see if it is relevant for them to create/request an account.