Improve creation of observable in getDriverStandings

[shonderdos]

For getDriverStandings we create a new observable for each new function call. Altough the unsubscribing is working fine. so we dont create memory leaks. It would be nice if we can create one observable that will stay open when navigating between pages.

[shonderdos]

We might not have to do this optimisation since firebase will check if the data is available locally. We can check that in the meta data. But we also first need to enable it which can be a different issue