Create application for gunicorn

This is apparently what gunicorn looks for.

Procfile

@@ -1 +1 @@
-web: gunicorn main:app --log-file -
+web: gunicorn csv_metadata_quality_web.main --log-file -

csv_metadata_quality_web/main.py

@@ -15,7 +15,7 @@ from flask import (
 )
 from werkzeug.utils import secure_filename
 
-app = Flask(__name__)
+app = application = Flask(__name__)
 app.config["MAX_CONTENT_LENGTH"] = 1024 * 1024
 app.config["UPLOAD_EXTENSIONS"] = [".csv"]
 # the only place we can write to on Google App Engine is /tmp