Implement bipartite property graphs and refactor graphviz bipartite graph methods

[slwu89]

Address #888

Please note the changes to https://github.com/AlgebraicJulia/Catlab.jl/pull/895/files#diff-77b8985182dac144d246a8e8f0becf17233222f79879274682b78adf2e454ca4 I suspect it was a typo that some small subset of the generic bipartite graph methods have argument type AbstractBipartiteGraph rather than HasBipartiteGraph (a narrower type instead of a wider type), so I changed that.

[github-actions]

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Tests

• New features and bug fixes have unit tests
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• Existing tests have not been deleted
• Code coverage >= 90% or reduction justified in PR

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