[ImgBot] Optimize images

*Total -- 112.72kb -> 78.91kb (30%)

/assets/img/nucleus-logo.png -- 51.93kb -> 26.59kb (48.8%)
/assets/img/icon_256x256.png -- 21.93kb -> 16.80kb (23.37%)
/assets/img/icon_128x128.png -- 10.13kb -> 8.25kb (18.55%)
/assets/img/favicon.png -- 4.10kb -> 3.71kb (9.64%)
/assets/img/icon.png -- 4.10kb -> 3.71kb (9.64%)
/assets/img/icon_180x180.png -- 20.53kb -> 19.85kb (3.31%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp