Merge branch 'backgroundjobs'

core/js/backgroundjobs.js

cron.php

db_structure.xml

lib/backgroundjob/queuedtask.php

lib/backgroundjob/regulartask.php

lib/backgroundjob/worker.php

lib/base.php

lib/public/backgroundjob.php

settings/admin.php

settings/ajax/setbackgroundjobsmode.php

settings/js/admin.js

settings/templates/admin.php