Passed token as parameter instead of using @Autowired of HttpSession to avoid issues with threads; defined custom Executor

Added input field for changing node name during copy of single nodes and added comments on moveOrCopyNodes method

Upload improvements: refactored upload logic into dedicated module (upload manager), handled deletion of node metadata for failed or aborted uploads, displayed proper error messages for the various cases

Set transfer target element as string instead of list of strings again. Used view with include param instead of custom protocol for async recall operations