Update flask-sqlalchemy to 2.3.0

[pyup-bot]

There's a new version of Flask-SQLAlchemy available.
You are currently using 2.1. I have updated it to 2.3.0

These links might come in handy: PyPI | Changelog | Repo | Docs

Changelog

2.3.0

---

Released on September 28, 2017

• Multiple bugs with __tablename__ generation are fixed. Names will be
  generated for models that define a primary key, but not for single-table
  inheritance subclasses. Names will not override a declared_attr.
  PrimaryKeyConstraint is detected. (541_)
• Passing an existing declarative_base() as model_class to
  SQLAlchemy.__init__ will use this as the base class instead of creating
  one. This allows customizing the metaclass used to construct the base.
  (546_)
• The undocumented DeclarativeMeta internals that the extension uses for
  binds and table name generation have been refactored to work as mixins.
  Documentation is added about how to create a custom metaclass that does not
  do table name generation. (546_)
• Model and metaclass code has been moved to a new models module.
  _BoundDeclarativeMeta is renamed to DefaultMeta; the old name will be
  removed in 3.0. (546_)
• Models have a default repr that shows the model name and primary key.
  (530_)
• Fixed a bug where using init_app would cause connectors to always use the
  current_app rather than the app they were created for. This caused issues
  when multiple apps were registered with the extension. (547_)

.. _530: pallets-eco/flask-sqlalchemy#530
.. _541: pallets-eco/flask-sqlalchemy#541
.. _546: pallets-eco/flask-sqlalchemy#546
.. _547: pallets-eco/flask-sqlalchemy#547

2.2

---

Released on February 27, 2017, codename Dubnium

• Minimum SQLAlchemy version is 0.8 due to use of sqlalchemy.inspect.
• Added support for custom query_class and model_class as args
  to the SQLAlchemy constructor. (328_)
• Allow listening to SQLAlchemy events on db.session. (364_)
• Allow __bind_key__ on abstract models. (373_)
• Allow SQLALCHEMY_ECHO to be a string. (409_)
• Warn when SQLALCHEMY_DATABASE_URI is not set. (443_)
• Don't let pagination generate invalid page numbers. (460_)
• Drop support of Flask < 0.10. This means the db session is always tied to
  the app context and its teardown event. (461_)
• Tablename generation logic no longer accesses class properties unless they
  are declared_attr. (467_)

.. _328: pallets-eco/flask-sqlalchemy#328
.. _364: pallets-eco/flask-sqlalchemy#364
.. _373: pallets-eco/flask-sqlalchemy#373
.. _409: pallets-eco/flask-sqlalchemy#409
.. _443: pallets-eco/flask-sqlalchemy#443
.. _460: pallets-eco/flask-sqlalchemy#460
.. _461: pallets-eco/flask-sqlalchemy#461
.. _467: pallets-eco/flask-sqlalchemy#467

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #558