Use tmp directory for extracting unmanaged files

During inspection unmanaged files are extracted to the file store
"unmanaged_files.tmp".
The directory gets renamed as soon as the inspection is finished.

This allows debugging after canceling the inspection and also prevents
overwriting of working data.
Mention tmp directory during unmanaged files inspection cancelation

Unmanaged files are now extracted to a temporary directory. If the user
cancels the process he gets a message where these partly extracted files
are available.