Merge branch '2.3' into 2.6

* 2.3:
  Changed PhpStormOpener to PhpStormProtocol
  [#5402] Being explicit what this applies to (it should not apply to things like >=)
  [Contributing] [Conventions] Added entry for Yoda conditions
  Document security.switch_user event
  Added some more docs about the remember me feature
  Fixed a minor grammar issue
  Fixed a minor grammar issue
  Added support for standard Forwarded header
  Added support for standard Forwarded header
  Fixed issues reported by @xabbuh
  Remove the Propel book chapter and explain why we do that

Author: weaverryan