Add button to clear all limits from search

Add a 'Clear limits' button to the catalog/index page within the
existing filter UI. The button is actually a link styled as a button,
since a real button sends a POST. The link redirects to the root path.
Add specs to feature test to verify functionality.

HYDRASIR-271 #close
Merge pull request #445 from projecthydra/feature/HYDRASIR-271

Add button to clear all limits from search