[many] Allow backup to operate on implicit order (c.f. #433)

beat/web/algorithms/migrations/0003_auto_20160701_1707.py

beat/web/common/models.py

beat/web/databases/migrations/0004_auto_20160701_1707.py

beat/web/databases/models.py

beat/web/dataformats/migrations/0002_auto_20160701_1712.py

beat/web/dataformats/models.py

beat/web/experiments/admin.py

beat/web/libraries/migrations/0003_auto_20160701_1707.py

beat/web/plotters/migrations/0003_auto_20160701_1707.py

beat/web/toolchains/migrations/0003_auto_20160701_1707.py

beat/web/utils/management/commands/backup.py

beat/web/utils/management/commands/beatdump.py