rose bush: take advantage of new tables in cylc suite run time database file

[matthewrmshin]

cylc/cylc-flow#1493 and cylc/cylc-flow#1503 introduce 3 new tables to the cylc suite run time database:

• broadcasts (see also cylc.rundb: new table for current broadcasts settings cylc/cylc-flow#1519)
• task_jobs
• task_job_logs

Rose Bush should take advantage of them:

• Display current and historical broadcasts in a table. (New page?)
• task_jobs should be much easier to query than task_events.
  • We should be able to write simpler SQL to get a job listing.
  • We should now be able to easily query timing information (rose bush: filter jobs by time run/updated #1308).
• task_job_logs will replace the log_files table in log/rose-job-logs.db.
  This table should be consulted first if it exists.
  We should only need to consult the log_files table in log/rose-job-logs.db
  to see if the file is in a tar archive or is removed.

We should probably have a listing of tasks, with their jobs grouped together.

• Job exit status does not always correspond to the task state.
• Some tasks may have no jobs! (See Task expiration. cylc/cylc-flow#1494 for example.)

[matthewrmshin]

The only thing left to do is to take advantage of task_job_logs, but this has a dependency on moving job log housekeeping functionality to cylc.

[matthewrmshin]

Now that I have thought about it, there is no reason why we have to wait for moving job log housekeeping functionality to cylc. We can make assumption by doing a quick file listing looking for log/job/CYCLE/ directories and log/job-CYCLE.tar.gz files.