[db] Add supported languages to the 'backend.Environment' model

beat/web/algorithms/migrations/0003_auto_20161123_1218.py

beat/web/backend/admin.py

beat/web/backend/api.py

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

beat/web/backend/migrations/0004_environmentlanguage.py

beat/web/backend/models.py

beat/web/backend/tests.py

beat/web/backend/utils.py

beat/web/code/models.py

beat/web/code/serializers.py

beat/web/libraries/migrations/0003_auto_20161123_1218.py

beat/web/plotters/migrations/0003_auto_20161123_1218.py