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