NetworkJobs: Propagator jobs keep others from expiring. #2155

In some owncloud server setups multiple concurrent connections for the
same session are not supported: owncloud/core#11153

This causes issues with multiple uploads and downloads. A usual symptom
is the quota job failing and the sync aborting.

This workaround lets activity on the propagator's GET and PUT jobs
reset the timeout of all network jobs. That way, queries like the quota
job would not time out while a large up/download is in progress.