dont set default locale in user.ui and use first browser locale by default if available and fall back to site default after that, fixes #1578; load locale from unjoined json files in debug mode

pandora/config.0xdb.jsonc

@@ -716,6 +716,7 @@
             "system": "0xDB@0xDB.org"
         },
         "https": true,
+        "locale": "en",
         "id": "0xdb",
         "name": "0xDB",
         "url": "0xDB.org",
@@ -803,7 +804,7 @@
             "listSort": [{"key": "director", "operator": "+"}],
             "listView": "grid",
             "lists": {},
-            "locale": "en",
+            "locale": "",
             "mapFind": "",
             "mapSelection": "",
             "page": "",