Re-home the URL path for the dashboard

[melange396]

As part of the content changes we have done recently, what was known as the "COVIDcast Dashboard" is now referred to as the "Delphi Epidata Dashboard". However, its URL still retains the "covidcast" text. Change this so that it resides at /dashboard instead. Create a forwarding alias from /covidcast to /dashboard so that it can still be reached by anyone with an old or bookmarked reference. Also be aware that the "COVIDcast Classic Dashboard" lives at a sub-path of the current dashboard URL and should remain at that location.