Implement maintenance command to delete orphaned data directories

Sometimes data directories of tasks remain on the disk, consuming unneeded disk space.

Therefore a service command to delete find and delete them is needed.

Currently callable from application root:

./translate5.sh task:clean

The tool may also delete hanging imports and tasks with status error. Just call it to see the capabilities.

In the future this will supersede the install-and-update.sh and will be callable with ./translate5.[sh|bat]