Bring back squisher

Some devices could benefit from the size reduction from running
squisher, so bring back a revised version as an optional part of the
build process.

This version of squisher no longer handles the process of making
release OTAs, instead operating on $OUT/system before system images and
OTAs are created.  This has the advantage of avoiding having to unzip a
just-packed OTA to optimize it before repacking it.

Change-Id: I288f694fd1bf26782e05dcfa797a0569d9fdf9cb
Fix Coloration

Signed-off-by: Chester Kener <Cl3Kener@gmail.com>
Use pngquant if installed

* Pngquant uses Lossless compression and does even more compression. Word on the street is it isn't noticeable.

Signed-off-by: Chester Kener <Cl3Kener@gmail.com>
Opticharger: Update Logic

* We can't assume the paths.  We must define dirname $DEFAULT_SYSTEM_DEV_CERTIFICATE

Signed-off-by: Chester Kener <Cl3Kener@gmail.com>
Update Header

* Forgot to include pngquant in the the file header so people are aware this version of opticharger uses pngquant as well.

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