fix dynamic table validation (#1741)

- dynamic table widget no longer creates a copy of field model, but
uses original one, fixes the problem with validation and state
management
- update unit tests

ng2-components/ng2-activiti-form/src/components/widgets/dynamic-table/dynamic-table.widget.ts

@@ -44,7 +44,7 @@ export class DynamicTableWidget extends WidgetComponent implements OnInit {
 
     ngOnInit() {
         if (this.field) {
-            this.content = new DynamicTableModel(this.field.form, this.field.json);
+            this.content = new DynamicTableModel(this.field);
             this.visibilityService.refreshVisibility(this.field.form);
         }
     }