Manage trade names

For managing trade names on taxon concept page I copied & adapted the existing functionality for synonyms, as that was quicker than adapting just selected functionality. I left out the 'new trade name' option from the taxon_concepts page though.

I added a delete button for any inverse relationships that  a taxon might have, for the purpose of allowing to delete an incorrect relationship. For example, it sometimes happens that synonym A is a synonym of a synonym B. Currently there's no way to see that from synonym B's page (because all content on that page is hidden for non-accepted names. maybe we should be showing it, but then we'd need to block all the 'new' buttons and thought maybe it's not worth it). Now at least you can delete the relationship from synonym A's page.