trello-169: add hyperlink for keyword to search by subject

This commit implements the keyword-search link from pull request https://github.com/datadryad/dryad-repo/pull/643 .

The update is available on dev currently, e.g.: http://dev.datadryad.org/resource/doi:10.5061/dryad.1159

This fix adds a hyperlink for a search to each keyword term, instead of a single hyperlink for all search terms.

The URL and search options for the keyword "KEYWORD NO SPACES" are:

http://datadryad.org/discover?query=&submit=Go
&fq=dc.subject:KEYWORD+NO+SPACES
&filtertype=*
&filter=
&rpp=20
&sort_by=score
&order=DESC
Don't hardcode the hostname -- causes problems when running on test servers! Start this URL with the /discover.