Run syntax/semantic validation for exported BEL Nanopubs.

[abargnesi]

While discussing the new OpenBEL Platform workflow, Justyna was concerned with exporting BEL Nanopubs that were invalid.

This work would be to provide an option to run syntax and semantic checks on exported BEL Nanopubs.

The user should be able to:

• Receive an export of only syntax-complete BEL Nanopubs.
• Receive an export of both syntax-complete and semantically-valid BEL Nanopubs.
• Receive a list of BEL Nanopub resources that failed syntactic or semantic validation (include resource locations for linking).