GNOM/ Make GNOLinkage extensible

[Override-6]

Currently, it's quite impossible to define its own Network Object Linker and to integrate it into the GNOM System.
Also, it should be much more easy for the user to retrieve an object from the reference.
Maybe making a MapNetworkObjectLinker that simply maps references to objects/presences.

[Override-6]

the GNOL Interface now contains the method addRootLinker that makes possible to inject a custom root linker in the General Network Objets Management

[Override-6]

Added MapNetworkObjectLinker that maps references to network objects.
A MapNetworkObjectLinker is used (optionally) for all objects and references that does not fit into any linker