Better log output of base URL.
Remove the default values for the custom OBA API server endpoint
preference that can be entered by the user.  When dealing with
multi-region, we only want to override the selected region and use a
custom-entered API endpoint when this preference has a value, and
therefore there shouldn't be any value stored by default.
Refactor getting preference for custom OBA API endpoint into RegionUtil
and remove unused imports.
Add local check on startup to see if user has entered custom API URL,
and if so don't make the Regions REST API call.
If user has entered custom API URL, then show the out of range dialog if
the user is out of range (previously, this wouldn't have been shown if
the user didn't have a region selected and had entered a custom API
URL).
For both map controllers, when the loader is called asynchronously from
UI events (e.g., map moved), before making a call to the OBA REST API
make sure that we either have a region selected or the user has entered
a custom OBA REST API URL.  This prevents unnecessary REST API calls to
a OBA server while we are trying to fetch the region info from the
Regions REST API asynchronously.