Add option to use Leiden algorithm in modularity.consensus_modularity()

[rmarkello]

The issue

The Louvain algorithm has some known deficiencies that can lead to badly connected (i.e., singleton or disconnected) communities. This is undesirable in many instances and can require using "bad" gamma settings when performing consensus community detection on certain networks to avoid such communities.

Proposed solution

The newly implemented Leiden algorithm proposes a solution to this issue of badly connected communities with the Louvain algorithm. Adding a parameter to the modularity.consensus_modularity() function to optionally use the Leiden algorithm would be awesome. Note, however, that the linked implementation is licensed under the GPL-3.0, so integrating it directly into netneurotools may not be desirable.