dcr features in pm4py ready for pr

[paul-cvp]

New features:

• DcrGraph objects: Distributed, Extended, Hierarchical, Timed, Import (from DCR Portal[1] and DCR js[2]), Export (to DCR Portal[2] and DCR js[2])
• Conformance: Alignments, Rule based
• Discovery with extensions: Role, Pending, Timed
• Visualization: DcrGraph visualization with graphviz
• Maturity notes: tests added for the dcr features, the code is documented with code comments

Contributors to this PR:
paul-cvp,Timmovich, Scones111, RagnarLaki,
simonhermansen, Axel, Tijs

[1]https://dcrgraphs.net/
[2]https://hugoalopez-dtu.github.io/dcr-js/