Back to uvicorn workers from eventlet.

The eventlet API has way too many dependency issues with gunicorn.

Still TODO: Fix or at least mitigate the WSGI workers timeout issue when
they handle websocket connections.

setup.py

@@ -63,10 +63,9 @@ setup(
         'alembic',
         'bcrypt',
         'croniter',
-        'eventlet',
         'flask',
         'frozendict',
-        'gunicorn @ https://github.com/benoitc/gunicorn/tarball/master',
+        'gunicorn',
         'marshmallow',
         'marshmallow_dataclass',
         'python-dateutil',
@@ -78,6 +77,7 @@ setup(
         'simple_websocket',
         'sqlalchemy',
         'tz',
+        'uvicorn',
         'websocket-client',
         'wheel',
         'wsproto',