Implements tests

[lenybernard]

• Dependency injection (parameters and services drived by configuration)
• Helper (each shortcut method will correctly add what is expected in the correct FlashBag)
• SessionHandler (what is in session is handled as well to be transformed into some template)
• Listener (on kernel.response, we correctly inject the templates into the page to show alerts ex. https://github.com/symfony/web-profiler-bundle/blob/2.8/Tests/EventListener/WebDebugToolbarListenerTest.php)
• TwigExtension (we can render alerts directly in twig thanks to this extension)