This PR was merged into the 2.3 branch.Discussion----------Javiereguiluz revamped quick tourHey 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 places2) Use "@stable" as the version constraint. I don't know of any drawbacks.Thanks!Commits-------1e36cfa [quick_tour] rewording and grammar fixes noted by@xabbuh69fdff1 [quick_tour] removed an unneeded comma30624eb [quick_tour] more rewording and grammar fixes0f13ce9 [quick_tour] rewording and grammar fixes suggested by@weaverryan7c0037e Restored all the original introductions for each tutorial partcb98a6c Restored the original line that explained how a routing file is imported from a bundlefdc755e Grammar fixes proposed by@weaverryan and@wouterjeca1e73 Added a more useful message for users that don't have PHP 5.4 and try to execute the server:run commanda013b11 Removed the animated GIF showing how to install Symfony985c68f Replaced "variable" by "placeholder" when using {_format} inside a route42bd69f Fixed the capitalization of a section heading75be815 Minor rewordingc1ad15d Added a new headline to better structure the documentationb16c3a2 Capitalized some sentences that come after a colon2fdcffd When using server:run command, it's not necessary to add the `app_dev.php` controller6afc80b Removed a wrongly inserted commae004661 Bundle names should not be placed in literals38b1292 [quick_tour] removed inline links81d6e20 [quick_tour] replaced "chapter" by "part" in some tutorial parts50e136c [quick_tour] second pass to "the architecture" chaptercdb7064 [quick_tour] second pass to "the controller" chapter and added a section about displaying error pages2cd3bab [quick tour] second pass to "the view" chapter4ad3c44 [quick_tour] second pass to the "big picture" chaptere7dfc8b [quick_tour] simplified "the architecture" chaptereb3fe4c [quick tour] simplified "the controller" chapterdbbc8c2 [quick_tour] updated "the view" chapter5b3a572 [quick_tour] finished the review of "The Big Picture" chapterf24eabc [quick_tour] updated some screenshots20e9fb0 [quick_tour] updated the "Controllers" section29992cd [quick_tour] simplified the "routing" sectiona84a556 [quick_tour] simplified drastically the first two sections of "The Big Picture" chapter