bug #4783 : Fix the notification to the users that have not enough right accesses to the commented content.

The concrete contents implement now the new method canBeAccessed().

For the majority, they just ask the ComponentAccessController if the specified user can access the Silverpeas application that manages them.
For those that use the PublicationDetail as their underlying content, their implementation belongs to the PublicationDetail one. In this implementation, the access rights are verified both on the application itself and on the nodes in which the publication is in (when there is a node).