fixes #718

So what we're doing here is that there isn't actually a method that says "show me the weighted hours that exist only in this department" so we go ahead and just calculate it and stick it on each ``Attendee`` object.

If this was something we wanted to do in multiple places, we'd probably make a custom filter for it so that we could access that from any Django template.  Since this is the only page that needs this information, putting the code in this page handler function seems sensible.