Nicer way to make task out of any callable

This commit introduces taskflow.functor_task.FunctorTask class, which is
adapter that can be used to make a task from any callable. Dependencies,
revert callable, name and version can be specified at the moment of
construction.

Partially implements blueprint refactor-decorators
Change-Id: If92de20a67ea6c228abb0a78edaa837b98581646