Implement sanitizer class
 - caches sanitizer config
 - supports list-view mode where links are filtered out so we don't get
   invalid, problematic html.
Address @janpaul123's comments
Deal with shared data structures more safely.
Tone rubocop's method length check down a little.
Merge pull request #73 from eMergence-by-Design/allow-links-in-stories

REVIEW: Implement sanitizer class