Implement multilayer community detection algorithms

[pitmonticone]

See De Domenico et al. (2015).

[TomKellyGenetics]

Suggestion. The following community detection algorithms are popular in social and life sciences.

Louvain algorithm (Blondel et al., 2008).
https://doi.org/10.1088/1742-5468/2008/10/P10008

Leiden algorithm (Traag et al., 2019).
https://doi.org/10.1038/s41598-019-41695-z

Note that the Leiden algorithm supports Multilayer graphs in R leiden and Python leidenalg. In principle it should be possible to port this functionality to Julia. It would take considerable effort but the performance advantages of Julia would be beneficial on large datasets (e.g,. single-cell transcriptomics and epigenomics).

[pitmonticone]

Thank you @TomKellyGenetics for your relevant suggestion.