improve migrations, dynamic label

...rations/0107_alter_districtcenterpage_content_and_more.py

...rations/0108_alter_districtcenterpage_content_and_more.py

shared/blocks.py

...rations/0040_alter_uniwebflexiblepage_content_and_more.py

...rations/0041_alter_uniwebflexiblepage_content_and_more.py