feat: use notifiers on schedule (#362)

* fix potential memory leak with time.After

* add new background service to manage scheduled notifications

* update docs

* remove old js reference

* closes #278

* tidy

backend/app/api/app.go

@@ -37,8 +37,11 @@ func new(conf *config.Config) *app {
 }
 
 func (a *app) startBgTask(t time.Duration, fn func()) {
+	timer := time.NewTimer(t)
+
 	for {
+		timer.Reset(t)
 		a.server.Background(fn)
-		time.Sleep(t)
+		<-timer.C
 	}
 }