give 100% points to people who click download links
refactor download points clicking to use backbone's native dom
events (and oh, use the content_view's set_progress method, not our
nonexistent set_progress method)
Merge pull request #2693 from aronasorman/give_points_to_downloads

give 100% points to people who click download links
only allow pdf point allocation when we're in a document and PDFJS isn't displayed