Cache leaf groups but no delete cache
Cache leaf groups with delete cache after save/create
Cache User#hidden and test it
Delete cache for User#hidden
Merge pull request #52 from fiedl/jb/638_cache_user_hidden

Jb/638 cache user hidden
Merge pull request #51 from fiedl/jb/638_cache_leaf_groups

Jb/638 cache leaf groups
Group#cached_leaf_groups: change cache key.