Allow users to manage their own cellar

- Allow users to add other users as friends
- All users (all access rights) can manage orders, bottles etc.
- Meta data (wine masters, wines, countries, producers etc.) can only be added or modified by admins; no other user must have permission to this
- Users can then view their own cellar
- Users can choose whether they make their cellar public
- Public cellars can be viewed by friends