Improve UI for empty states - Empty layout

Overview

Starting from an empty canvas should be an inviting experience that encourages a user to start adding components. Currently, it's very far from that and actually just looks kind of broken.

Proposed resolution

Introduce a special case/design for when editing a page that doesn't yet have any components on it. There should be empty UI designs for both the layers panel and the preview itself.

User interface changes

Current, poor UI