Update the license header

[vttranlina]

Currently, most source code files not contain license header.

Some files have an Apache header copied from the James project.

We need to add the GNU license header to all our files.
(comment: #1354 (comment))

Retained attribution:

/***************************************************************
* As a subpart of Twake Mail this file is edited by Linagora.                            *
*                                                                                                                                   *
* https://twake-mail.com/                                                                                      *
* https://linagora.com                                                                                            *
*                                                                                                                                  *
* This file is thus subject to The Affero Gnu Public License version 3.          *
*                                                                                                                                  *
* https://www.gnu.org/licenses/agpl-3.0.en.html                                             *
*                                                                                                                                  *
* This program is distributed in the hope that it will be useful,                     *
* but WITHOUT ANY WARRANTY; without even the implied warranty of     *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the     *
* GNU Affero General Public License for more details.                                    *
*                                                                                                                                  *
* This file was taken and adapted from the Apache James project                *
*                                                                                                                                  *
*    https://james.apache.org                                                                                 *
*                                                                                                                                  *
* It was originally licensed under the Apache V2 license.                                *
*                                                                                                                                  *
*    http://www.apache.org/licenses/LICENSE-2.0                                             *
*                                                                                                                                  *
 ***************************************************************/

We shall add in all of our files also the following header I believe:

/***************************************************************
* As a subpart of Twake Mail this file is edited by Linagora.                            *
*                                                                                                                                   *
* https://twake-mail.com/                                                                                      *
* https://linagora.com                                                                                            *
*                                                                                                                                  *
* This file is thus subject to The Affero Gnu Public License version 3.          *
*                                                                                                                                  *
* https://www.gnu.org/licenses/agpl-3.0.en.html                                             *
*                                                                                                                                  *
* This program is distributed in the hope that it will be useful,                     *
* but WITHOUT ANY WARRANTY; without even the implied warranty of     *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the     *
* GNU Affero General Public License for more details.                                    *
 ***************************************************************/