Merge branch '2.7' into 2.8

* 2.7:
  Added 'default' color
  [HttpFoundation] Reload the session after regenerating its id
  [HttpFoundation] Add a test case to confirm a bug in session migration
  [Serializer] Fix ClassMetadata::sleep()
  [2.6] Static Code Analysis for Components and Bundles
  [Finder] Command::addAtIndex() fails with Command instance argument
  [DependencyInjection] Freeze also FrozenParameterBag::remove
  [Twig][Bridge] replaced `extends` with `use` in bootstrap_3_horizontal_layout.html.twig
  fix CS
  fixed CS
  Add a way to reset the singleton
  [Security] allow to use `method` in XML configs
  [Serializer] Fix Groups tests.
  Remove duplicate example
  Remove var not used due to returning early (introduced in 8982c32)
  [Serializer] Fix Groups PHPDoc
  Enhance hhvm test skip message
  fix for legacy asset() with EmptyVersionStrategy
  [Form] Added upgrade notes for #15061

Author: fabpot

ParameterBag/FrozenParameterBag.php

@@ -69,4 +69,14 @@ public function set($name, $value)
     {
         throw new LogicException('Impossible to call set() on a frozen ParameterBag.');
     }
+
+    /**
+     * {@inheritdoc}
+     *
+     * @api
+     */
+    public function remove($name)
+    {
+        throw new LogicException('Impossible to call remove() on a frozen ParameterBag.');
+    }
 }