Change the graph created by "gg BA" on the m0 first nodes.

In the Barabási-Albert model, we need a arbitrary graph of m0 nodes, to start with, and the only constraint is that each node has an edge (i.e. link to a neighbor). For the moment, in the graph generated by using gg BA ..., the base graph is a star of m+1 nodes.

The goal is to change this base graph, allowing the user to choose the graph they want, and to set the base graph to a clique by default.

Stephan Devismes suggested to use the following syntax to allow the user to choose the graph they want :

m0:(a1,a2);(b1,b2);(c1,c2)...

with m0 being the number of nodes, and (a1,a2) meaning there's a link between the node of index a1 and the one of index a2