make the ttl for the storage mapping of the root storage much higher

[icewind1991]

Because groupfolders all share the root storage id, the list of mapping for it can get quite long.
But since groupfolder access is also not likely to change often we can probably just cache that for much longer

• properly detect what the storageid for the root storage is instead of just assuming 1
• look into some kind of mechanism to flush the cache on groupfolder related changes