Wait for app to be stable before creating intervals

While working on #748 (closed) and with a hint from @kresset I found an issue:
on Pat-side currently it was never checked for updates, because there were intervals created before the app is stable.

We need the app to be stable before checking for updates. At least that's what I read somewhere a long time ago… I think.

I added a function isApplicationStable(applicationRef: ApplicationRef) in the utils - if you know a better place please tell me - and now wait in the necessary sections of the app.