linking to pfam from motif details table #156

- because of whitespace change, please try view the diff through https://github.com/WormBase/website/compare/staging...pfamxref?w=1  the ``?w=1`` added to the url makes github ignores white space difference

- in addition, I modified macro match_link to 1) match ignore case 2) return a false value if nothing is matched
- I also modified macro external_urls, so it falls back to external base url