Website: Make npm and Bower install instructions easier to find.

- Update the README to remove hard-coding a version and instead link to the
  website download page.  This avoids having version mismatches during
  publishing.
- Update the Downloads page to move npm/Bower instructions to the top.  Put
  latest release version in the page description for better visibility.
Merge pull request #239 from nicksay/readme-links

Website: Make npm and Bower install instructions easier to find.