implemented observable types for live updates

src/test/mod.rs

@@ -0,0 +1,13 @@
+use crate::app::rx::Observable;
+
+#[test]
+fn test_observable() {
+    let mut observable: Observable<u32> = Observable::new();
+
+    observable.subscribe(|value| {
+        assert_eq!(5, value);
+    });
+
+    observable.next(5);
+}
+