Adding count of instructors to "all events" page.

There isn't room to display all the instructors next to the event on the "all events" page, so this displays a count instead, and highlights workshops that are missing instructors.

1.  Modify `all_events` function to decorate event objects with number of instructors.
2.  Modify view to display those counts.
3.  Modify base `_page.html` to load CSS to highlight events with no instructors.
Adding people to event display.

This PR adds a table of people involved in a workshop to the event's display.
Fixing issues based on @wking review
Merge pull request #112 from gvwilson/11-add-instructor-names-to-event

Adding count of instructors to "all events" page.