User permission support

[mirceaalexandru]

we can do it like this:

1. add permissions to each user from a set of defined permission types.
2. create groups with set of permissions and then assign users to groups.
3. mix of the above, so you can assign an user to a group and then override a certain permission specially for that user by direct assigning of that permission. This method offers a greater flexibility and also allows us to implement in two stages - first directly assign permission and in another iteration add group support.
4. Other approaches?