[ImgBot] Optimize images

*Total -- 40.79kb -> 35.33kb (13.37%)

/build/icons/16x16.png -- 2.15kb -> 0.93kb (56.94%)
/build/icons/32x32.png -- 3.05kb -> 1.71kb (43.93%)
/build/icons/64x64.png -- 5.17kb -> 3.94kb (23.7%)
/build/icons/128x128.png -- 9.82kb -> 8.92kb (9.09%)
/build/icons/256x256.png -- 20.60kb -> 19.83kb (3.74%)