Search by common names

This pull request enables the search by common names for species plus, displaying matches in the dropdown menu and in the results page.

It also removes the Checklist::TaxonConceptPrefixMatcher and changes the checklist autocomplete to use Species::TaxonConceptPrefixMatcher, since both Species+ and the Checklist are matching the autocomplete results in the same fields (synonyms, english, french and spanish common names).

To test this you might need to clear your cache:
Rails.cache.clear