Add pipeline validation (interpreting, not runtime)

[Melevir]

All items in pipeline list should exist as callables with pipeline type decorator.

[Melevir]

All items in pipeline list should exist as callables

This is done in https://github.com/best-doctor/Mario/commit/84380d711e1637a9ed7c3b29718ab78327f9ffae.

with pipeline type decorator.

This is tricky to implement on class initialization, so lets move this validation to flake8-super-mario (see #16).