Fix subspecies links

This is mostly to fix issue reported in https://www.pivotaltracker.com/story/show/66931774

However, it was too tempting not to fix a couple of other things a s well.

Because the focus was on links, I replaced the old way of rendering links on search / taxon pages by regular query params aware link-to's; that should help users navigate the page using multiple tabs.

On another note, when hitting a taxon page the site would make 3 requests instead of 1. The 2 additional requests were supressed:
-> a request to api/v1/taxon_concepts - that was running because the taxon_concept route was nested under taxon_concepts - unnested that
-> a request to auto complete - that was running in response to populating the search field with the full name of the searched taxon - created an intermediate property which does not trigger a request
-> moved the spinner showing / hiding logic from controllers to routes (tried to use the loading route functionality, but gave up on that as I couldn't get it to work exactly like the current solution) 

There were also some smaller changes to simplify the code.