refactor: refactor SCThingTypes from union-type to enum. SCThingType-type-attributes are now string-type-attributes.

src/core/protocol/routes/bulk/BulkRequest.ts

@@ -13,7 +13,6 @@
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
 import {SCAbstractRoute} from '../../../Route';
-import {SCThingTypes} from '../../../Thing';
 import {SCISO8601Date} from '../../../types/Time';
 
 /**
@@ -45,9 +44,11 @@ export interface SCBulkParameters {
   source: string;
 
   /**
-   * Type of things that are indexed in this bulk
+   * Type of things that are indexed in this bulk.
+   * 
+   * String is an element of the SCThingType enumeration.
    */
-  type: SCThingTypes;
+  type: string;
 }
 
 /**