Fix CSV Generation

Update the headers to be based on the taxonomy defined in the
columns[:iczn_groups]
Fix links for CSV download and 'Link to this search'

Remove params_for_search - it had a lot of hard coded values, just
replaced with reusing the params hash after removing the
authenticity_token (which is not used in GET requests)
Merge pull request #44 from NESCent/fix_csv_download

Fix downloading of search results as CSV