Configured $wgJobBackoffThrottling

* Also tweaked $wgJobTypesExcludedFromDefaultQueue to be global
  for gw* jobs, so the nextJobDB.php does not direct runners there
  when they do any of those jobs anyway.

Change-Id: I9a96da7c0369164ba3d9ccedb4a7db6a32343734
Merge "Configured $wgJobBackoffThrottling"