GET: Retry if bad range header used. #2280

* If a 416 is returned and we used a Range header, try again
  from scratch.
* The direct URL logic was also inconsistent for resumed downloads:
  it sent the Range header but didn't check the returned
  Content-Range header correctly. Now resuming is disabled for
  direct URL downloads.

(cherry picked from commit 48d3c75745e15033f46806fd2386e8ca32d16091)
Download: Don't store message body if status != 2xx #2280

(cherry picked from commit 705cd571a59d1fba6225f9b11bafd6acd17cd434)
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.

(cherry picked from commit 2eec85a97cdf6e32be368de631fa7a3899740c06)