improve rendering speed by caching LevelGeometry in database

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

@@ -0,0 +1,9 @@
+from django.core.management.base import BaseCommand
+
+
+class Command(BaseCommand):
+    help = 'rebuild level geometries'
+
+    def handle(self, *args, **options):
+        from c3nav.mapdata.render.base import LevelGeometries
+        LevelGeometries.rebuild()