ISIS-964, ISIS-969: rename @ClassLayout to @DomainObjectLayout; introduce @DomainServiceLayout and move @DomainService(menuBar=... over to it) and replace DomainServiceFacet#getMenuOrder() with DomainServiceLayout#getMenuOrder().

Also updated ServicesInstallerFromAnnotation that reads directly from the annotation (no facets are available at the point at which it runs).