convert django lazy string proxies to strings in the base schema validator, rather than in the serialization code of each source model

src/c3nav/mapdata/utils/locations.py

@@ -416,7 +416,7 @@ class CustomLocation:
 
     @cached_property
     def grid_square(self):
-        return grid.get_square_for_point(self.x, self.y) or ''
+        return grid.get_square_for_point(self.x, self.y)
 
     @cached_property
     def title_subtitle(self):

src/c3nav/mapdata/utils/user.py

@@ -17,13 +17,13 @@ def get_user_data(request):
     }
     if permissions:
         result.update({
-            'title': str(_('not logged in')),
+            'title': _('not logged in'),
             'subtitle': ngettext_lazy('%d area unlocked', '%d areas unlocked', len(permissions)) % len(permissions),
             'permissions': tuple(permissions),
         })
     else:
         result.update({
-            'title': str(_('Login')),
+            'title': _('Login'),
             'subtitle': None,
             'permissions': (),
         })