The PHP_CSS_Parser is added as a git submodule to the CSS Extension.
The given PHP code- parser_demo.php is a script takes input a CSS file
and uses the parser to parse the CSS file. It removes all the
background attributes and displays the modified CSS file

Change-Id: I87e286bd3f3e62e23f75c4343999e2f10e745964
(cherry picked from commit 34cb320507afed74f6ac4fac57cc6e11f9f35869)
Reviewed-on: https://gerrit.wikimedia.org/r/94761
Reviewed-by: GICodeWarrior <gicodewarrior@gmail.com>
Tested-by: GICodeWarrior <gicodewarrior@gmail.com>