Remove the _no_quadtile versiond of the selection routines and switch
to using the ordinary ones but with a (large) limit applied on the size
of the area to prevent us spending ages working out the list of tiles
to be selected.
Use a preinitializer to load the settings from application.yml so
that they are available as early as possible. All settings can also
be overridden using environment variables.
The ad-hoc settins in environment.rb are then moved to this new
system so we have one consistent location for settings.
