Add better relation support

Logic/FeatureSource/RegisteringFeatureSource.ts

@@ -0,0 +1,19 @@
+import FeatureSource from "./FeatureSource";
+import {UIEventSource} from "../UIEventSource";
+import State from "../../State";
+
+export default class RegisteringFeatureSource implements FeatureSource {
+    features: UIEventSource<{ feature: any; freshness: Date }[]>;
+
+    constructor(source: FeatureSource) {
+        this.features = source.features;
+        this.features.addCallbackAndRun(features => {
+            for (const feature of features ?? []) {
+                if (!State.state.allElements.has(feature.feature.properties.id)) {
+                    State.state.allElements.addOrGetElement(feature.feature)
+                }
+            }
+        })
+    }
+
+}