move blueprints in dedicated folder

app/blueprints/contributions/__init__.py

@@ -0,0 +1,23 @@
+from flask import Blueprint
+from flask_login import login_required
+
+
+bp = Blueprint('contributions', __name__)
+
+
+@bp.before_request
+@login_required
+def before_request():
+    '''
+    Ensures that the routes in this package can only be visited by users that
+    are logged in.
+    '''
+    pass
+
+
+from . import (
+    routes,
+    spacy_nlp_pipeline_models,
+    tesseract_ocr_pipeline_models,
+    transkribus_htr_pipeline_models
+)