title: Sylius: Overwrite BackendMenuBuilder
body: <p>I start developing a project based on Sylius and after install process I want to customize Backend Dashboard. As Sylius works with services, I found that BackendMenuBuilder is a service called "sylius.menu_builder.backend". With this in mind and some googling I edited my "services.yml" in AppBundle/Resources/config" and put this lines:</p>
  
  <pre><code>services:
      sylius.menu_builder.backend:
           class: AppBundle\Menu\Backend\BackendMenu
  </code></pre>
  
  <p>I created a new class "BackendMenu" in "AppBundle\Menu\Backend" to be called instead the "default" Sylius service. I've got some error in my first tries but after I could overwrite the default service in this way. Is this the right way to do that? For any new service that I want to not use the default version should I insert this new parameter in my "services.yml"? I wonder this because I think developing a medium/big project over Sylius platform and maybe it could be a handy problem.</p>