[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

demo-shell-ng2/app/components/files/files.component.ts

@@ -150,12 +150,8 @@ export class FilesComponent implements OnInit {
         dialogRef.afterClosed().subscribe(folderName => {
             if (folderName) {
                 this.contentService.createFolder('', folderName, this.documentList.currentFolderId).subscribe(
-                    node => {
-                        console.log(node);
-                    },
-                    err => {
-                        console.log(err);
-                    }
+                    node => console.log(node),
+                    err => console.log(err)
                 );
             }
         });