Redesign side panel.

[gleachkr]

The current implementation is pretty ad-hoc and ugly. I think the best way to proceed will be to stick to the 1/2 widget layout, but to

• [x] redo some spacing and css
• [x] add a widget-buttons component that controls the focus of the single widget layout (continue to hide this on scroll in mobile)

This would be a minimal redesign. Eventually you should be able to

• https://github.com/opentower/populus-viewer/issues/43