Add roles with permissions

[odungern]

Add the possibility to define roles with their permissions. The permissions shall support inheritance: For example a read permission at project root is a read permission on every item, except if a different permission is given in the children hierarchy.

There are 2 inheritance hierarchies, which must both grant a certain permission to become effective:

• Project <-- ResourceClass/StatementClass <-- PropertyClass ... to control permission by class
• Project <-- Hierarchy <-- Folder <-- Resorce Reference ... to control permission within the hierarchy tree

Each permission is a vector of Create, Read, Update and Delete permissions to allow a fine-grained access control on property level.

[odungern]

I will submit a design proposal in the near future.