Leaderboard does not show progress or failures

[fcaps]

Since we have a cache-looser, it can take a while to load the entries.
This will result in a page, that just shows a empty list for a couple of seconds without telling the user to wait.

Acceptance Criteria:

• opening the leaderboard will show a loader if a request in due
• changing the leaderboard to "2v2" etc. will also show a loader
• failed request will be handled and show the user something like a error message

non-goals:

• fixing the leaderboardRepository if the token is invalid (currently creating a 503 on stale token)