Group actions by category.
Improve layout for different page widths.
Fix navbar collapse.
Further improvements to action layout.
Make actions selectable.
Simplify action elements.
Reformatting for readability.
Define my-section-header directive.

- Separates icon and title cruft into separate template file.
- Sections' default open states and titles are defined in datamodel.
Define my-action-list directive.

- Renders sequence of action images with optional functions for
  calculating CSS classes and handling clicks.