Introduced named repositories (avoids repeated entry of urls);
simplified DirectorArguments and InstallArguments by removing factory
methods (constructor is used instead by clients); using properties
instead of fields where appropriate in combination with
@TupleConstructor; @Immutable classes have read-only properties (using
final); DirectorArguments and InstallArguments both delegate to new
RepositoryDelegate class to remove duplicate code (RepositoryDelegate
makes use of new Repository class); renamed InstallableUnitArguments to
InstallableUnit