Adjust error_reporting to allow deprecation messages for 3.0
Merge branch '2.7'

* 2.7: (65 commits)
  Configure firewall's kernel exception listener with configured entry point or a default entry point
  PSR-2 fixes
  [DependencyInjection] make paths relative to __DIR__ in the generated container
  [FrameworkBundle][Router Cmd] use debug namespace.
  [FrameworkBundle] Update deprecated service call
  Fix PHP Fatal error:  Cannot call constructor in symfony/console/Symfony/Component/Console/Helper/DialogHelper.php on line 37
  Removed a dev annotation from a version constraint
  Fixed the syntax of a composer.json file
  Fixed the symfony/config version constraint
  Tweaked the password-compat version constraint
  Docblock fixes
  Append to PR #12737 referring Ticket #12704
  Issue #12658 Add a deprecation note about Translator's setFallbackLocale...
  Issue #12606 Adding warning logs about the deprecation of [...]/Tests/FormIntegration...
  Hackday deprecated 12621
  Added deprecation log for validate and validateValue on ExecutionContext...
  [Console] [Hackday] [2.7]  Add a deprecation note about ProgressHelper
  [Hackday][2.7] Add a deprecation note about MetadataInterface's accept() method
  [Validator] Added a deprecation note about setPropertyAccessor #12698
  [Locale] Adding a deprecation note about the Locale component
  ...