Code to define modeltype RM-2380

create a modeltype table used by models and pfts. The table is
initialized with the types already in the models (not pfts). All models
and pfts are associated with a modeltype next.
User can add/edit modeltypes and see the pfts/models associated with it.
Although it may be impossible to add a model type with a NULL name via the BetyDB web interface, I'd still add ", :null => false" here because if there _does_ happen to be a model type with a NULL name, it breaks a lot of pages.