Add show route and refactor authority/controller interface

The Authorities how have a different interface with the controller.
Making a new authority object will no longer do a search---call #search
to do that. Can also call #get_full_record for show information.

sub-authorities support can still be improved. Some authorities allow
no sub-authority, while others demand one. The code allows both, all the
time.

More tests on the show route are needed. I wasn't sure how to test it.
Merge pull request #35 from projecthydra/show-refactor

Add show route and refactor authority/controller interface