Switching to lazyload for getting the next job query

 Testing showed that lazyload is apparently fastest in our specific case since we only fetch a single job here and there's only one child table, hence only two simple queries vs. subqueryload which issues as second more complex query or joinedload which issues a single more complex join.

Removed an unnecessary status == None check since status will never be None. (Will add this db restraint as well in the migration commit coming soon.)