Helper functions for graph composition

[slizzered]

Assuming structure where a new graph is created through a root node that consists of N homogeneous substructures, it would be very convenient to have a function that automates this process.

• Also think about interconnects!

example interface:

Graph substructure;
// ... definition of substructure

Graph g = consistsOf(substructure, N);

//Alternatively:
Interconnector intcn; // functor determines how the N substructures will be interconnected
                      // could be fully-connected, hypercube, etc.
Graph g = consistsOf(substructure, N, intcn);

[slizzered]

This is mostly done through the new interface that uses inheritance and children. Interconnect nodes are created automatically, the interconnects have still to be done by hand (see new issue about bidirectional edges)