* 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
