Fixes for skip-nav link, RSS feeds, hidden labels
Expanded link text (whole sentence, vs "here")
Added a self-hiding header to Stats table, for assistive tech
Alt text and new-window msg for CC-0 and Open Data (data package pages)
Consolidating all CC-BY links in page footers.
Merge remote-tracking branch 'origin/jima-accessibility-sweep' into dryad-master
Removed "accessibility-hidden" tag

The tag wasn't being processed correctly by the page rendering system,
and it wasn't strictly necessary.