added: ModelEnv class - now Model has a pointer to ModelEnv
and ModelEnv has a pointer to ModelData, model_connector_mode, table_index and doc_field_pointer
git-svn-id: svn://ttmath.org/publicrep/morm/branches/join_models@1191 e52654a7-88a9-db11-a3e9-0013d4bc506e