#21 Group access rights

[Oliver Wihler]

For the company picture site I would like to make certain galleries
available to 3rd parties.

So, in addition to Administrator and View roles, the administrator
can create new groups.

By default a picture can be seen by only the creator. Creator can
add view privileges to Groups or the world.

Access rights can also be applied to galleries. All pictures in that
gallery automatically inherit the gallery permissions.