JPEGs compressed with lossy compression

All JPEGs compressed either with 90% (some logos & screenshots) or 80% (photos and remaining logos/screenshots) quality compression.
Average saving in file size was between 30% and 70% saving!
(images folder as gone from 12.1Mb to 7.5 Mb)
ImageOptim GUI tool was used - uses the JPEGOptim, JpegTran and JpegRescan libraries.

HAVEN'T YET CHECKED in browser - Make Watch was crashing for me! Don't mind if you do this, or if I do @jamesshedden ...

I'll make another PR next week for PNGs when I get onto them...