add heavy caching to mapdata api

src/c3nav/mapdata/management/commands/clearmapcache.py

@@ -0,0 +1,11 @@
+from django.core.management.base import BaseCommand
+
+from c3nav.mapdata.lastupdate import set_last_mapdata_update
+
+
+class Command(BaseCommand):
+    help = 'Clear the map cache (set last updated to now)'
+
+    def handle(self, *args, **options):
+        with set_last_mapdata_update():
+            pass