Add web front-end and fix API issues

node_modules/concurrently/dist/lib/observables.js

@@ -0,0 +1,20 @@
+import { fromEvent, share } from 'rxjs';
+const sharedEvents = new WeakMap();
+/**
+ * Creates an observable for a specific event of an `EventEmitter` instance.
+ *
+ * The underlying event listener is set up only once across the application for that event emitter/name pair.
+ */
+export function fromSharedEvent(emitter, event) {
+    let emitterEvents = sharedEvents.get(emitter);
+    if (!emitterEvents) {
+        emitterEvents = new Map();
+        sharedEvents.set(emitter, emitterEvents);
+    }
+    let observable = emitterEvents.get(event);
+    if (!observable) {
+        observable = fromEvent(emitter, event).pipe(share());
+        emitterEvents.set(event, observable);
+    }
+    return observable;
+}