[FLINK-4647] Read bipartite graph

[mushketyk]

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[greghogan]

There are some refactorings in #2832 which overlap with updates here.

[greghogan]

#2832 has been committed to master. Please rebase.

[mushketyk]

Hi @greghogan ,

I've rebased this PR on top of master.

[greghogan]

@mushketyk what do you think of refactoring GraphCsvReader and BipartiteGraphCsvReader to use configuration objects using the builder patter? It would be nice to have CsvReaderConfiguration in core Flink but we could add it to Gelly first.

GraphCsvReader currently have two of everthing (fieldDelimiterEdges/fieldDelimiterVertices, ignoreCommentsEdges/ignoreCommentsVertices, ...). BipartiteGraphCsvReader looks to add three of the same. We could look into collapsing these into a single configuration object.

[aljoscha]

I'm closing this as "Abandoned", since there is no more activity and the code base has moved on quite a bit. Please re-open this if you feel otherwise and work should continue.