[#2956] Refactoring the scopes entry entirely to not talk about the request anymore, since it has a simpler solution

See sha: b84f52c28d969b5143521261d818105824eaea5e for more information.
[#2972] Many small tweaks - thanks very much to @WouterJ and @xabbuh
[#2972] Clarifying how to use the request_stack with an example
Merge pull request #2972 from symfony/scope-refactoring

[#2956] Refactoring the scopes entry