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 within mlSearch);
* authRestored -> `appInitialized` promise to resolve in `layout` state --
simplifies and hardens process of ensuring the application is ready when
first loaded or refreshed, including that we have restored an active session
if there is one;
* rewrite explore state (and add new exploreResults state) to better
handle state, routing and events;
* minor css changes;
* watch specific directories in dev-tasks so that other directories under
dev-tasks do not cause an extra watches