WIP: Replace loading notification with a spinner
This is mostly ready, but it doesn't make sense to merge it now, since the collection loading is so slow.
- Crossfade transition currently employs a hack. This will need to be fixed. Alternatively, we can do crossfade for collection from/to game transition as well, in that case the hack will not be needed.
- This exposes #98 (closed) particularly badly, as it happens 90% times with Games view right after loading.
- Test how it interacts with empty state.
- Test this with opening URIs directly.
This will allow us to fiх #105 cleanly later.