Add caching into local storage for a faster map experience

Logic/FeatureSource/LocalStorageSaver.ts

@@ -0,0 +1,35 @@
+/***
+ * Saves all the features that are passed in to localstorage, so they can be retrieved on the next run
+ *
+ * Technically, more an Actor then a featuresource, but it fits more neatly this ay
+ */
+import FeatureSource from "./FeatureSource";
+import {UIEventSource} from "../UIEventSource";
+
+export default class LocalStorageSaver implements FeatureSource {
+    public static readonly storageKey: string = "cached-features";
+    public readonly features: UIEventSource<{ feature: any; freshness: Date }[]>;
+
+    constructor(source: FeatureSource) {
+        this.features = source.features;
+
+        this.features.addCallbackAndRun(features => {
+            if (features === undefined) {
+                return;
+            }
+            if(features.length == 0){
+                return;
+            }
+
+            try {
+                localStorage.setItem(LocalStorageSaver.storageKey, JSON.stringify(features));
+            } catch (e) {
+                console.warn("Could not save the features to local storage:", e)
+            }
+        })
+
+
+    }
+
+
+}