improved uploading of files (#1730)

* improved uploading of files

- new core/UploadDirective to allow dropping files to any html element
- enhanced file dropping for DataTable rows (disabled by default)
- enhanced file dropping for DocumentList rows (disabled by default)
- upload drop area now handles file uploads for child elements (i.e.
rows in the document list)

* fix unit tests

* unit tests and code cleanup

* #1732, fix upload of folders

ng2-components/ng2-alfresco-datatable/src/components/datatable/datatable.component.ts

@@ -51,6 +51,9 @@ export class DataTableComponent implements AfterContentInit {
     @Input()
     contextMenu: boolean = false;
 
+    @Input()
+    allowDropFiles: boolean = false;
+
     @Output()
     rowClick: EventEmitter<DataRowEvent> = new EventEmitter<DataRowEvent>();