title: Retrofit2 parallel response handling with observables
body: <p>I'm working on an app where a user can edit his/her profile after registration. The problem is that editing the profile uses multiple API calls to the backend. One for editing email, one for editing password so on and so on. I'm using retrofit2 in conjunction with RxJava so the calls are Observables/Singles. A spinner is shown when a user presses the edit button and the calls are executed on different threads. How do I handle the successes/fail if they are executed in parallel? The user needs to know if an edit was a success or not and also hide the spinner when the calls have been completed. I can't use combineLatest because the user may opt to change only their email or profile picture or name so only those will be called and not all of them.  </p>