Maps is a helper class of static methods for working on and with maps
(name/value pairs) and sets - primarily to allow convenient static programatic loading.
Interface is used by inner classes of migration classes to define a
migrate method used to move to a more recent version of a DAO that has
been updated.
When a database object class needs to change, copy it as an inner
class into the Migrations class in the same package and have it
implement Migration.Interface.