Event start/stop and a static event info page

Primarily this branch is about addressing #71. Now, events that have not started yet will load in an inactive mode, with a drop down pane that can show static HTML. This is controlled by the 'description' field on an event, which can be edited in the standard event admin interface. When an event is live, that about panel can be shown and hidden as desired by users.

This was primarily requested by OKFN for their event.

Fixes #21, too.