Javiereguiluz revamped quick tour

Hey guys!

See #3562 - this is the same, but rebased against the 2.3 branch.

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets |

Off of the top of my head (but I could be wrong), the only thing that was 2.4 specific is the version number used in the composer.phar create-project command. We could fix this in 2 different ways:

1) Don't fix it - just always keep that number updated to the latest released version. We do this similarly in other places

2) Use "@stable" as the version constraint. I don't know of any drawbacks.

Thanks!