Reflect SE changes

[wouterj]

As of 2.5, the SE doesn't come with the AcmeDemoBundle. You have to use the SensioDistributionBundle for that: symfony/symfony-standard#643

We should at least update the quick tour and maybe take a look at other places if we need to tell something about this or tweak the text a little bit.

[cordoval]

also let's add if possible the option to how to decouple form sensiodistribution to do our own distros i mean not project skeletons but distro packages rather than letting it be a bundle 👶

[fabpot]

So, here are the changes:

• When using create-project, Composer will ask you whether you want to install the demo bundle or not;
• When depending on symfony/framework-standard-edition, the demo bundle is indeed not available anymore (but nobody should do that anyway)
• When downloading a package from symfony.com, the demo bundle will still be available.

So, the impact is pretty minimal.

[wouterj]

Thanks @fabpot That is indeed less than I thought. So what we have to do:

• The quick tour should be updated to add info about the question whether you want the demo or not
• Important places where we reference the Demo bundle, mostly the Book chapters, will need an update. For instance, "In the DemoBundle, you can see XXX" should be updated to "If you installed the DemoBundle, you can see XXX".

[wouterj]

Sicne #3874 fixed this and a new installer is introduced, I think it's valid to close this issue.