[ImgBot] Optimize images (#348)

*Total -- 7,376.32kb -> 5,550.67kb (24.75%)

/extra-textures/background/panorama_4.png -- 6.60kb -> 2.82kb (57.3%)
/screenshot.png -- 3,902.90kb -> 2,647.10kb (32.18%)
/assets/favicon.svg -- 4.88kb -> 3.31kb (32.09%)
/extra-textures/loading.png -- 88.28kb -> 66.53kb (24.64%)
/assets/favicon.png -- 28.32kb -> 22.43kb (20.8%)
/extra-textures/gui.png -- 36.68kb -> 29.68kb (19.07%)
/assets/invsprite.png -- 3,308.66kb -> 2,778.79kb (16.01%)

Signed-off-by: ImgBotApp <[email protected]>
Co-authored-by: ImgBotApp <[email protected]>

Author: LEGALISE PIRACY