cleanup and optimize shell-mommy.sh, compress image

[Ven0m0]

LC_ALL=C is often used in scripts since ASCII is slightly faster than unicode (might not be beneficial here, got the idea from neofetch originally). Webp is smaller than png and has wide browser support. Furthermore since most linux systems have bash, the script can be shortened with some bashism's to be more compact/optimal. This also makes the script more robust (e.g [[...]] instead of [...] to work with checks and variables more safely.