feat($ui): Added a simple stream implementation to support dynamic UI

src/behavioral-subject.ts

@@ -0,0 +1,18 @@
+export class BehavioralSubject<A> {
+    private subscribers: Array<(value: A) => void> = [];
+    private _value: A;
+
+    constructor(value: A) {
+        this._value = value;
+    }
+
+    next(value: A) {
+        this._value = value;
+        this.subscribers.forEach(observer => observer(this._value));
+    }
+
+    subscribe(observer: (value: A) => void) {
+        observer(this._value);
+        this.subscribers.push(observer);
+    }
+}