Write validator

[cmungall]

@putmantime made a start here #29

The validator may work by connecting to an instance (eg via BOLT) OR by downloading using kgx script and running checks locally / in-memory e.g using networkx

[putmantime]

The current validation in KGX uses the network x object (currently from the Neo4J transformer), and procedurally checks nodes and edges with Python. Extending this conversation to discuss adding an RDF specific validation method like ShEx.

@amrapalijz
@amalic
@stuppie
@andrawaag
@cmungall
@balhoff

[deepakunni3]

The validator was completed, thanks to @lhannest @hsolbrig @putmantime