Issue #2380389 by webflo, Mile23, davidwbarratt, timmillwood, hussainweb, tstoeckler, bojanz, yched, MKorostoff, alexpott, webchick: Use a single vendor directory in the root

Issue #2571817 by Cottser, hussainweb: Remove race condition handling in TwigEnvironment::loadTemplate(), it's fixed upstream now

Issue #2568171 by Cottser, dawehner, hussainweb, Wim Leers, cilefen, znerol: Upgrade to Twig 1.22 and implement our own cache class

Issue #2568085 by plach, alexpott, dawehner, Berdir: Lock Twig on ~1.21.2 until we are able to upgrade to 1.22.0

Issue #2444615 by borisson_, neclimdul, jibran, dawehner, jhedstrom, Fabianx: Move testing packages to require-dev in composer.json

Issue #2546618 followup by plach: Document that we don't depend on the Symfony Translation component.

Issue #2546618 by plach, dawehner, chx, bojanz: Replace the Symfony Translation component with a custom interface since we don't use it

Issue #2105825 by cosmicdreams, larowlan, hussainweb, Nitesh Sethia, dawehner, naveenvalecha, iMiksu: Update Doctrine/common Component to 2.5.1 (security) (includes cache/annotations too)

Issue #2546272 by hussainweb, jhedstrom, dawehner: Update guzzlehttp/psr7 to 1.2.0 and guzzlehttp/promises to 1.0.2

Issue #2498599 by Cottser, naveenvalecha, webchick, karolus, cilefen: Remove sdboyer/gliph since it is unused by core

Issue #2493911 by dawehner, larowlan, damiankloip, hussainweb, jibran, cilefen, benjy, iMiksu, mtdowling: Update guzzle, goutte and mink-goutte-driver to the latest release