MEF Element Attribute Inheritance

[rakhimov]

The MEF element attributes carry extra data about elements.
Moreover, attributes (data) are inherited from containers
(fault-trees, event-trees, components, model)
by elements defined within those containers.
The element definitions can also override attributes.

The MEF attribute inheritance requires
keeping track of ancestor-containers to descendant-elements relations.
If a container's attribute changes,
its descendant-elements' attributes must be updated accordingly (a la prototype).

Required by #193