Better Site searching

[dshoreman]

Rather than showing a list of filtered sites to the left of the preview/editor pages, the search bar should just use a Search Selection dropdown from Semantic. That way the full page width can be dedicated to the site being viewed or edited, and results will only be shown when the search bar is focused.

On the list page it may be worth keeping the cards, but we need to make sure the issue where filtered sites aren't updated on creation is solved. When you type a name and create it, the filter remains set to the name while the search box is cleared. What should happen is both get cleared after creation, so the site list shows all sites again.