LP#1848550: client-side caching of org settings for AngularJS

LP#1848550: client-side caching of org settings for AngularJS

The web client almost always does live lookups any time it needs to
check an org setting.  But these settings rarely change, so it would
make sense to cache them.  They're already cached using Lovefield in
order to support offline; this commit checks the cache first, and only
does a live lookup if the setting is uncached or expired (i.e. added to
cache more than 12 hours ago).  Offline ignores the 12-hour expire time
so that we always have settings to work with when the server is
unreachable.

Signed-off-by: Jeff Davis <jeff.davis@bc.libraries.coop>