Add ability to delete a carrel

[dbrower]

[dbrower]

Running into problems that the webui does not have file permissions to delete carrel files. It looks like the compute code assigns all carrel files to have owner "eric":

drwxr-xr-x. 16 eric eric 4096 May 26 17:44 dogs

The webui can read the files but not delete them. The carrel records are removed from the database, but if the carrel is not removed from disk it will reappear the next time the background process scans the private carrels, a process that occurs every 5 minutes.