Highlight active secondary nav item.
Fix border for when exhibit pages are longer than exhibit page content, apply fixes to mobile views: clear exhibit pages, remove column borders, add more margins for single column content, remove borders from admin bar items.
Constrain logo image to width of the browser.
Clear exhibits on browse when using pagination, fix exhibit page navigation to display third-level child pages and only show page tree for current section, remove top border from featured exhibit on browse view.
Merge branch 'master' into pmj-museums