Add alembic database migrations

[JWCook]

Closes #211

• Set up database migrations with alembic
• Split initial revision into multiple revisions based on commit history
• Update revisions after initial state to not fail if columns already exist (to handle manually/partially updated dbs)
• Add nox shortcut for alembic autogenerate
• Include alembic revisions in PyPI package
• Add migrate() function for other libraries/applications to use
  • Handle databases previously created without alembic
  • Stamp current alembic head revision in create_tables()
  • Handle alembic script location for both package and repo
• Use prek instead of pre-commit in noxfile