Double composition restored (aka Entity and CompositeEntity restored
instead of Actor).

Most of methods added in Entity, Port, Relation, CompositeEntity, but
none of the their implementations has been done (just headers).

Added four protected functions in NamedObj: add, remove, get, getList;
since every instance of NamedObj operates on a collection of NamedObj
(eg, Entity has a list of Ports) they should implement their
functionalities abstractly (ie, add a NamedObj to a list of NamedObj) so
they could be used in derived classes (eg, addPort method of Entity
reuse add method of NamedObj). They must be implemented in further
revisions.

No other major changes.