Add temporary command to migrate data for "areas"

This will be run with a CSV of all broadcast messages. Since very
few users are creating or updating broadcasts, it's highly unlikely
we'll encounter a race condition during the update.

app/commands.py

@@ -11,5 +11,22 @@ def list_routes():
         print("{:10} {}".format(", ".join(rule.methods - set(['OPTIONS', 'HEAD'])), rule.rule))  # noqa
 
 
+@click.command()
+@click.argument('csv_path')
+@with_appcontext
+def tmp_backfill_areas(csv_path, dry_run=True):
+    import csv
+
+    from app.models.broadcast_message import BroadcastMessage
+
+    for id, service_id in csv.reader(open(csv_path)):
+        message = BroadcastMessage.from_id(id, service_id=service_id)
+        print(f'Updating {message.id}')  # noqa
+
+        if not dry_run:
+            message._update_areas(force_override=True)
+
+
 def setup_commands(application):
     application.cli.add_command(list_routes)
+    application.cli.add_command(tmp_backfill_areas)