Initial implementation of action-based engine

This is first in series of changes that provides separation of flows into
engines and pattens. Patterns define structure, while engine define how
the task should be run according to said structure.

This change adds the basic patterns and a very simple engine that
is able to run flow defined with patterns by converting it to recursive
structure of so-called 'actions'.

For simplicity and ease of review certain major features like
resumption, saving and passing on task results and notifications are
left out for farther changes.

Partially implements blueprint patterns-and-engines

Co-authored-by: Anastasia Karpinska <akarpinska at griddynamics.com>
Change-Id: I68515d8a5b30d5d047bf9beb67cc3e2111175190