feat(filter-date-range): Explore Docs by Date Range

Enable filtering and faceted search of date ranges by last activity
date.

This commit also includes refactoring and other supporting changes:

* mlUtil: date helper functions — subject to change based on design
around time zones
* overhaul faceted search (support shadow configuration)
* authRestored -> promise to resolve in states, simplifies process of
ensuring that we know if the user is logged in
* rewrite explore state (and add new exploreResults state) to better
handle state and events
* minor css changes
correct navigational errors

* go to '/' when the app title is clicked
* use appRouting to initiate change to tag filter from results
* properly reload results on search
* remove incomplete styling from tags in results, as they are now
expected to work
IN-PROGRESS: refactor mlModel stuff