Small tweaks to the event admin page

Here are some of the changes that I've had floating around on a branch for a while. I'm trying to make the workshop admin page easier to manage. This changeset gives more visibility into student/coach numbers, as well as indicating who's new (I like to use this page to check people in to the event). I've also commented the Gemfile, to make it easier for new developers to figure out what's going on.