Add more information about failing steps in low verbosity output
Import django modules only if they are used.

This commit solves the issue #407.
Add tests for model update functionality
Filled in functionality for model update
Pulled run_scenario into a shared func in dill tests
Add negative test for DB update
Added test for diffirent update syntax
Added negative test for update without PK
Fix test order
Implement the update functionality
Changed the name of create things to write things
Add API compatibility wrappers
Add docs to reference writes_models decorator
Update doc for write_models
Reverted API change in test to make sure that API compatibility is preserved
Tests for new update by field functionality
Fix API compat properly
Replaced simple update by pk with update by arbitrary field
Add default value for field (None means create op)
Add test for trying to update a model with only creates_models decorator