Download files with nginx

@antgonza helped with this one.  Remaining to be done:

~~Get nginx into Travis CI~~ (EDIT: We are deferring this for now, since we don't know what to do at this time)
- [x] Add download links in the GUI where appropriate
- [x] Fix whatever tests are about to fail when I submit this PR
Woops -- thought this was the other comment thread. What I should have said is that I went with the first approach you suggested, which works fine.  Commit is coming soon, I just didn't want these comments to disappear