Add a "view usage terms" button

[mcannon068nw]

Add a button somewhere on the front page labeled "View Usage Terms" that triggers the medical disclaimer pop-up. Currently this pop-up only triggers the first time a user triggers the page and disappears until they clear their cache/cookies. We should have this there to allow people to view the terms at any time.

[obigriffith]

I would suggest we go further than this. A "View Usage Terms" doesn't necessarily evoke medical disclaimer. We want this to always be clearly visible or clearly viewable. Check out CIViC to see how this handled.

[jsstevenson]

We can probably just put it on the footer, right?