[ADF-643] upload enhancements (#1949)

* rework folder uploading

- flatterns hierarchy on folder upload
- performs a single traversal for the entire folder heirarchy and ends with a comple file list
- allows now dropping folders on existing folders
- overall code improvements

* fix unit tests

* readme updates

* clean old and unused code

* code cleanup

* limit concurrent uploads

* update code as per review

* fix upload button for Safari

* fixes for Safari

- Safari compatibility
- code updates based on review

* fix code

* fix unit tests

ng2-components/ng2-alfresco-upload/src/components/upload-drag-area.component.ts

@@ -39,6 +39,12 @@ export class UploadDragAreaComponent {
     @Input()
     enabled: boolean = true;
 
+    /**
+     * @deprecated Deprecated in 1.6.0, you can use UploadService events and NotificationService api instead.
+     *
+     * @type {boolean}
+     * @memberof UploadButtonComponent
+     */
     @Input()
     showNotificationBar: boolean = true;