Add translatable strings to memorial field (#734)

data/fields/memorial.json

@@ -1,5 +1,20 @@
 {
     "key": "memorial",
     "type": "combo",
-    "label": "Type"
+    "label": "Type",
+    "strings": {
+        "options": {
+            "blue_plaque": "Blue Plaque",
+            "bust": "Bust",
+            "cross": "Memorial Cross",
+            "obelisk": "Obelisk",
+            "plaque": "Commemorative Plaque",
+            "sculpture": "Sculpture",
+            "statue": "Statue",
+            "stele": "Stele",
+            "stolperstein": "Stolperstein",
+            "stone": "Stone",
+            "war_memorial": "War Memorial"
+        }
+    }
 }