Optimize all the PNG files (average of 76% reduction)
Created by: alfrix
This makes theme changing noticeably faster and may help platforms with limited storage.
I couldn't detect any noticeable changes in quality but theme makers should double check @baxysquare @kivutar @Tatsuya79 @rutantan
Commands used (also stated in the commit)
pngquant.exe --skip-if-larger --quality=70-85 pngquant.exe --skip-if-larger --ordered --speed=1 --quality=70-90 optipng.exe -o=7