Refactor: Use new logging mechanism from Context
o element.py / plugin.py: Removed supporting logging code, and derive
the log handle from Context.
o _scheduler/scheduler.py, _scheduler/queues/queue.py: Adapt to new Job initializer API for the logfile
o _scheduler/jobs/job.py: Run job activities within the new context manager
which turns on logging for a job. Also removed a lot
of custom logging abstract methods which are unneeded.
o _scheduler/jobs: Job implementations need not implement so much custom logging.
8 files changed
