Properly stop list jobs on close

Track running jobs in JobTracker. On its destruction (i.e. UI is going down) we kill and delete (which waits for finishing) those jobs.

Tested with very big tar.gz (libarchive plugin) and .zip (cliplugin) and it closes without crashing now

Acked by rakuco
BUGS: 193908
FIXED-IN: 4.13.2
REVIEW: 118108