[experiments] Refactoring: Rename the possible statuses of a Block

beat/web/algorithms/models.py

beat/web/backend/models.py

beat/web/backend/tests.py

beat/web/experiments/migrations/0008_block_status.py

beat/web/experiments/models/block.py

beat/web/experiments/models/cached_file.py

beat/web/experiments/models/experiment.py

beat/web/experiments/serializers.py

beat/web/experiments/signals.py

beat/web/experiments/tests.py

beat/web/libraries/models.py

beat/web/reports/tests.py