big renaming of hive->worker, analysis_job->job, analysis_job_file->job_file, analysis_job_id->job_id, worker.beekeeper->worker.meadow_type, etc

testing the idea of analyses that can be empty for blocking purposes (it does not block while it is empty)

bugfix: alldead mode did not set cause_of_death; now it sets it always to FATALITY (yes, there is certainly a better solution)

job_error table now holds jobs' termination messages; workers do not die when jobs die, but can be instructed to to so

adding a silent option (do not try to synchronize too much when the hive load is too high) and maximise_concurrency option (try to run as many concurrent analyses as possible instead of lots of jobs of one single analysis)

Added an optional Bio::EnsEMBL::Analysis argument to get_num_needed_workers subroutine, to only get the number of workers needed for this analysis