Added the download of csar_files

fixes #25 
* Added the functionality for downloading csar_files to the ui and the backing bean
* Replaced the treetable with the grouped datatable and removed the TableRow class thatis no longer necessary
* Changed the DownloadCsarService to use UUIDs
* Changed the FileSystem to use UUIDs
* Added the use of UUIDs to the UploadCsarService