Set "active-graph" cookie on the server when there is a request

[david-yz-liu]

Right now the cookie is only set on the client. But, students can access URLs of the form /graph?dept=CSC. The server should correctly look up the right graph and set the cookie then.

See public/js/graph/setup.js lines 29-40. This should be replaced because the active-graph cookie should be set.

Also, we'll need to store the short form "CSC" for different departments to get the correct graphs.