Update license in install files and check for url writing

This PR adds a front route /empty that returns a 204. It is used to check in the end.php page of the install process if the rewriting module of the HTTP server is enabled.
Moreover it replace all the header comments with the new Thelia one ( LGPL license ).
It should complete #573 

	modified:   core/lib/Thelia/Controller/Front/DefaultController.php
	modified:   local/modules/Front/Config/front.xml
	modified:   web/install/bdd.php
	modified:   web/install/bootstrap.php
	modified:   web/install/config.php
	modified:   web/install/connection.php
	modified:   web/install/end.php
	modified:   web/install/footer.php
	modified:   web/install/header.php
	modified:   web/install/index.php
	modified:   web/install/permission.php