Revert "[Form] Remove "value" attribute on empty_value option"

This reverts commit 9e849eb78bcc668a2b8aad39cb47e2ad32c73a47.

Reasons for the revert:

* https://github.com/symfony/symfony/issues/8478
* https://github.com/symfony/symfony/issues/8526
[Form] Removed the "disabled" attribute from the placeholder option in select fields due to problems with the BlackBerry 10 browser
moved some fixed dep versions from 2.2.* to ~2.2 (refs #8613)
Merge branch '2.2' into 2.3

* 2.2:
  [HttpKernel] added a missing dep for dev
  [Form] fixed wrong call to setTimeZone() (closes #8644)
  Fix issue with \DateTimeZone::UTC / 'UTC' for PHP 5.4
  [Form] Removed the "disabled" attribute from the placeholder option in select fields due to problems with the BlackBerry 10 browser
  [routing] added ability for apache matcher to handle array values
  removed dead code and fixed CS
  [Validator] fixed StaticMethodLoader trying to invoke methods of abstract classes (closes #8589)

Conflicts:
	src/Symfony/Bundle/TwigBundle/TokenParser/RenderTokenParser.php
	src/Symfony/Component/Form/FormConfigBuilder.php
	src/Symfony/Component/HttpKernel/composer.json
	src/Symfony/Component/Validator/Tests/GraphWalkerTest.php
Merge branch '2.3'

* 2.3:
  moved some fixed dep versions from 2.2.* to ~2.2 (refs #8613)
  [HttpKernel] added a missing dep for dev
  [Form] fixed wrong call to setTimeZone() (closes #8644)
  Fix issue with \DateTimeZone::UTC / 'UTC' for PHP 5.4
  [Form] Fixed patched forms to be valid even if children are not submitted
  Revert "[Form] Fix of "PATCH'ed forms are never valid""
  [Form] Fixed: If a form is not present in a request, it is not automatically submitted
  Fixes link indices
  [Form] Removed the "disabled" attribute from the placeholder option in select fields due to problems with the BlackBerry 10 browser
  Revert "[Form] Remove "value" attribute on empty_value option"
  [routing] added ability for apache matcher to handle array values
  removed dead code and fixed CS
  [Validator] fixed StaticMethodLoader trying to invoke methods of abstract classes (closes #8589)