Add new role VoObserver

- add new Role VoObserver to object Role in PerunBeans
- add this role to all privilege tests (in core methods) where voAdmin has rights to read (get information)
Add new role VoObserver in AuthzResolverBlImpl

- add VoObserver to isAuthorizedForAttribute method
- Add voObserver role to isAuthorized method
Changes in methods get/setAttributeRights

- method setAttributeRights will aplicate the same rights for VoAdmin - Read and VoObserver - Read for the attribute
- Add information (javadoc) about behavior with VoObserver to the method getAttributeRights
- Add information (javadoc) about behavior with VoObserver to the method setAttributeRight
- VoObserver rights are special and are not returned by method getAttributeRights (changes in BlImpl)
Merge pull request #112 from stavamichal/newRole-VoObserver

New role vo observer