Reset the box model to content-box in the web debug toolbar

This makes the styles compatible with CSS frameworks changing the box
model to box-sizing using a universal selector (Bootstrap 3 for instance).
Merge branch '2.3' into 2.4

* 2.3:
  Fixed typo
  [validator] throw an exception if isn't an instance of ConstraintValidatorInterface.
  Reset the box model to content-box in the web debug toolbar
  [FrameworkBundle] Allowed "0" as a checkbox value in the php template.
  raising delta on stopwatch as travis really breaks with less than 35
  Switched to correct gender of "Token"
  fixed typos in several translations
  [HttpKernel] use static late binding when dumping out container