Feature 4148 New cryptographic function: a variation of SHA-512

To toughen the encryption of passwords, a new cryptographic algorithm is added: a variation of SHA-512 as used in the Unix systems.

Refactoring of the authentication classes used in the authentication mechanism: their name indicates what is their responsibility, clean up the code to be more comprehensible, move to the new package org.silverpeas.authentication. Only old codes for which I don't know if they are yet used are stayed in place in the old package com.stratelia.silverpeas.authentication.

Merge the code of Yohan from the Silverpeas master.