Adds delete button to the collections#show view

Although the collections#index view had a delete button, the
collections#show view was missing the delete button.  Copied
the button_to code from #index to #show.  Modified the
spec/features/collections_show_spec.rb to have a visit test.

HYDRASIR-16 #close
Merge pull request #395 from projecthydra/HYDRASIR-16-collections

Adds Delete button and action to collections#show for HYDRASIR-16