Update to beat.core 1.6.x and beat.backend.python 1.5.x

beat/web/backend/helpers.py

beat/web/backend/management/commands/qsetup.py

beat/web/backend/models/job.py

beat/web/backend/tests/common.py

beat/web/backend/tests/test_helpers.py

beat/web/backend/tests/test_scheduler.py

beat/web/backend/tests/test_setup.py

beat/web/databases/admin.py

...eb/databases/migrations/0004_beat_backend_python_1_5_x.py

beat/web/databases/models.py

beat/web/databases/signals.py

beat/web/experiments/models/experiment.py

buildout.cfg