JSON: Transmit the ID as a string. See commit for the reason.

src/main/java/ch/fritteli/labyrinth/generator/renderer/json/Generator.java

@@ -20,7 +20,7 @@ class Generator {
     @NonNull
     JsonLabyrinth generate() {
         final JsonLabyrinth result = new JsonLabyrinth();
-        result.setId(this.labyrinth.getRandomSeed());
+        result.setId(String.valueOf(this.labyrinth.getRandomSeed()));
         result.setWidth(this.labyrinth.getWidth());
         result.setHeight(this.labyrinth.getHeight());
         final List<List<JsonCell>> rows = new ArrayList<>();

src/main/java/ch/fritteli/labyrinth/generator/renderer/json/JsonRenderer.java

@@ -39,7 +39,7 @@ public class JsonRenderer implements Renderer<String> {
         rows.get(0).add(cell);
         // Wrap it all in an instance of JsonLabyrinth.
         final JsonLabyrinth jsonLabyrinth = new JsonLabyrinth();
-        jsonLabyrinth.setId(0L);
+        jsonLabyrinth.setId("0");
         jsonLabyrinth.setGrid(rows);
         return jsonLabyrinth;
     }

src/main/resources/labyrinth.schema.json

@@ -12,8 +12,8 @@
   ],
   "properties": {
     "id": {
-      "type": "integer",
+      "type": "string",
-      "existingJavaType": "java.lang.Long"
+      "description": "64 bit precision signed integer value. Transmitted as string, because ECMAScript (browsers) don't normally handle 64 bit integers well, as the ECMAScript 'number' type is a 64 bit signed double value, leaving only 53 bits for the integer part, thus losing precision."
     },
     "width": {
       "type": "integer",