Add new Phenotype Class

[creisle]

In order to support loading the Human Phenotype ontology (see https://hpo.jax.org/) and linking these terms from CIViC statements it would be helpful to add a phenotype class to GraphKB. This will require

• Define the new class in this package
• Add a migration to GraphKB API to apply/create the new class
• Ensure this new class is included in the class-based permissions object

This new class should subclass ontology