[chore:] added IsGermany()-function

DataStore/DataStructures.cs

@@ -180,6 +180,17 @@ public class KasPerson
 
     public string used_plz { get; set; } = "";
 
+    public bool IsGermany()
+    {
+        var trimmedLand = (land ?? "").Trim();
+        var trimmedLowerLand = trimmedLand.ToLower();
+        var isGermany = trimmedLowerLand == "germany" || trimmedLowerLand == "ger" ||
+                        trimmedLowerLand == "" || trimmedLowerLand == "de" ||
+                        trimmedLowerLand == "deutschland";
+
+        return isGermany;
+    }
+    
     public static void SetUsedPLZ(int id, string plz)
     {
         foreach (var set in Settings._instance.addressSets.addresses)