Fix EZP-22128: Change license & copyright info to refer to root file

Update inline copyright and license infor to refer to LICENSE file.
Makes it easier to maintain source code across licenses and easier
to keep on updating the copyright year.

The format here is same as used in Symfony.
Merge pull request #132 from ezsystems/license-EZP-22128

EZP-22128: Centeralize Copyright & License info