* feat(field-level-lineage): adding models for field level lineage
adding models for field level lineage. Introduce DatasetFieldUrn as a unique identifier for dataset field
Move code to linkedin/datahub-gma.
"GMA" (Generalized Metadata Architecture) is the backend of DataHub, and has been moved to its own repository.
This deletes the code that was moved and uses jars that GMA publishes to bintray to load it.
Note that not all of GMA was moved, but most of it. We may still move more things to the other repository in the future.
