Add LazyVal class (lazy loading of values)

helpers/LazyVal.ts

+class LazyVal<T> {
+    private val: T = null;
+
+    constructor(private valLoader: () => Promise<T>) {}
+
+    get value(): Promise<T> {
+        return new Promise<T>(async (resolve) => {
+            if (this.val === null) {
+                this.val = await this.valLoader();
+            }
+
+            resolve(this.val);
+        });
+    }
+
+    reset() {
+        this.val = null;
+    }
+
+    get isValueLoaded(): boolean {
+        return this.val !== null;
+    }
+}
+
+
+export default LazyVal;