Feature 4147: management of a cipher symmetric key for content encryption

This feature is for managing a cipher symmetric key in order to encrypt and to decrypt some confidential contents. The content encryption will be itself provided by another feature.

The key is for the cipher AES-256 bits. This cipher requires the installation of the unrestricted Java cryptographic policy from the Oracle website.
The key isn't generated but it is passed in hexadecimal by a Silverpeas administrator through a dedicated web page. The key will be then protected by a CAST5 encryption and stored in Silverpeas.

Don't forget to merge also the branch feature-4147 in Silverpeas-Components and in Silverpeas-installer-package.