[simulation mode] implement mock context manager

Context manager is responsible for providing a valid context with
   corresponding attributes and functions for the current object.
   Modified context manager will be used for mock implementation. It will be
   inherited from the original one and will be called ``MockContextManager``.
   It will store instructions which objects or classes are needed to be
   replaced with mocks and return context with mock definition instead of the
   original function. For that purpose several dictionaries should be used:
   one for mapping objects with mocks and other one for class mapping.