Aqueduct

- removed event loop stopping after Flow stopping
- added StopTask forwarding to all steps

- updated multiprocessing module
- added environment checks
- revised Aqueduct errors
- removed pytorch dependency
- revised Flow stopping

- change queues to multiprocessing.Queue

- add processes liveness checking

- fixed `_task_states` clearing

- add timeout_sec for process method
- spawner moved from Torch and tuned for logger integration like Sentry
- new few `__str__` and `__repr__` for more readable exceptions context
- add some graceful terminating