Multiple genomes for a sequence

For a guide referenced in multiple genomes:

1. Two attributes

• Sequence.genome -> Sequence.genomeRef: Genome @relationship(type: "HAS_REF", direction: OUT)
• Sequence.genomes: [Genome!] @relationship(type: "HAS_SEQUENCE", direction: IN)

2. or:

• add an attribute is_ref in HAS_SEQUENCE relationship
• Sequence.genome -> Sequence.genomes: [Genome!] @relationship(type: "HAS_SEQUENCE", direction: IN)