Preset/stolperstein: Make preset EU only

Following https://github.com/openstreetmap/id-tagging-schema/pull/964#pullrequestreview-1541084558

- rename file to follow convention that locationSets should be part of the filename
- add Q46 which represents europe

Code via https://location-conflation.com/?locationSet=%7B%20include%3A%20%5B%27q46%27%5D%20%7D%0A

data/presets/historic/memorial/stolperstein-EU.json

@@ -21,5 +21,10 @@
         "historic": "memorial",
         "memorial": "stolperstein"
     },
-    "name": "Memorial Plaque Stolperstein"
+    "name": "Memorial Plaque Stolperstein",
+    "locationSet": {
+        "include": [
+            "Q46"
+        ]
+    }
 }