Refactor file up- and download

The up- and download file code in FileService was not written with servers in mind it seems. Hardcoded paths and pre-pended with ./ to eliminate the option of full paths. The test was apparently with hardcode path as well; regardless of what the config file said. Test does not check whether the produced zip is actually correct. In addition it would be nice if the download would not be a zip for a single file and in the future viewable in the browser for select files.