Blacklight update and visual enhancements

--Added date range limit facet for refining search results
--Added validation for date range limit facet
--Added language facet for refining search results
--Added origin place facet link when there's only one place
--Implemented user account feature to support a signed-in state, allows
individual sign-ins, password reminder dispatch, search history review
and to search save functionality
--Added user utility navigation element to global page layout
--Added sign in link to global footer
--Added new styles to support signed-in state and related views
--Removed the "beta" status alert ribbon from global layout
--Corrected layout rendering issue with IDS download component
--Improved layout rendering for mobile/smart displays
--Inserted an "ad" for CURIOSity collections into search results layout
--Added helper text for users when searches yield no results
--Corrected JS issue with accordion behavior in results facet rail
--Cleaned up solr_document.rb to remove unused code and add comments
--(VC) Updated Gem vulnerabilities devise and updated gems for rails,
mysql, blacklight gems
--(VC) Updated the release number to use the current blacklight version
6.20
--Added guided tour modal window functionality for PDS served documents
--Added style refinements for date range facet limiter
--Revised sign-in behavior so that users are returned to their search
results after successful login instead of the homepage