#28 privacy management at the server level

[Sandy El Helou]

Adding visibility attributes to 3A items (public, private, closed)
Adding permissions table (with right_type and status-only for spaces)
adding method at the model level to check access right (viewer, contributor, member) actor has an access over a item ( preview for closed items, viewer, contributor, member)
adding method at the model level to get list of spaces members (those who confirmed), owners, viewers ( invitees), contributors etc
method to get viewers of an actor's profile

[Sandy El Helou]

and adding method to get access list for an item