Added demo route

@cwshevlin @nshah20 @LoRyder1 

Howdy, fellow ExitSlippers!  As an job-seeker, I would like to be able to have a demo route to link peeps to rather than telling them "go to sign in, enter case-e....." etc.  In this pull request, I've added another route at "/demo" that will log into an account and redirect to what that person would see upon login.  Is that cool with you guys?

If it is, I need whoever is in charge of the Heroku account to add this environment variable:  DEMO_EMAIL=case-eee@yahoo.com.

If it's not... :(