Get rid of graph-tool dependency

[Thomasillo]

Find some other (possibly pure python but fast) tool to replace graph-tool or write the needed feats self.

Features from graph-tool that are needed:

• Delete degree zero nodes
• Delete self loops
• Detect (and treat) parallel edges
• Calculating graph Laplacian,
• Calculating graph Adjacency matrix
• (both as sparse matrices pls)
• Edge filtering

[Thomasillo]

https://docs.scipy.org/doc/scipy/reference/sparse.csgraph.html ?