M3 results display improvements

This branch addresses several, but not all, issues in m3 relating to:

- Adding selected metadata fields to display in summon and aquabrowser results (a more through job will be helped by reviewing the logic in the NCSU code around displaying results.)  Created a helper function to support more easily extracting MARC fields and subcodes from Aquabrowser results.
- Handling the case of "no results" by presenting a message and a link (added settings for "plain" URLs to each resource)
- Truncating (with ellipsis) long titles and descriptions
- Infrastructure to support passing selected settings upon rendering pages
- Some cleanup of aquabrowser query results parsing logic in views.py