Use community detection class hierarchy in Cython
Use community detection class hierarchy in Cython

This ports the class hierarchy that is used for the community detection
algorithms to Cython and thus greatly reduces the Cython code for the
community detection algorithms.

fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit