Support for exporting data flow slice to age and neo4j format

For apache age, there is a csv format for loading graphs

https://age.apache.org/age-manual/master/intro/agload.html

Support graphml format to export the DataFlows slice. Must be usable with filtering #4.

https://neo4j.com/docs/apoc/current/import/graphml/

My preference would be graphml so that it could be imported using python networkx directly.

https://networkx.org/documentation/stable/reference/readwrite/graphml.html

Finally, add a section on README explaining the steps involved to export, import and query the information.