Re-commit partial completion of #42: Refactor docstrings according to PEP 257 using "pep257":
* defaults.py: template_session
* filters.py: pop_self
* filters.py: fill_empty
* helpers.py: *_app
* helpers.py: console_command
* helpers.py: get_kwargs

Additional updates:
* Change obscure and long names to shorter and consistent names
* The updated names are only up to the currently modified functions