Opticharger: Add Pngquant

Pngquant is a revolutionary lossy .png optimizer that shrinks files up to 70% (see http://pngquant.org/)

I personally feel that users should have this option because it will shrink ROM size an additional couple of megabytes if installed.  I don't notice any graphical difference but if you do you can simply uninstall pngquant and it will revert to using optipng or whichever other png optimizer you have installed.

Change-Id: I904cf0634a58d8fa8d95396c47409402220375ae
Signed-off-by: Chester Kener <Cl3Kener@gmail.com>