Losslessly optimise file size of mod assets

[NeRdTheNed]

TODO:

• .ogg files - currently trying to revive Segher Boessenkool's ReHuff program, need to implement more Vorbis parsing options.
• .json files? (haven't investigated yet :P)

Optimised, not yet properly tested and verified:

• Losslessly reduced file size of all .png files: This was achieved through using “Papa’s Best Optimizer” (which can be downloaded from https://papas-best.com/optimizer_en) with “Optimise compression”, “Delete metadata" and “Clear transparent (premultiplied) pixels” selected, as well as "ImageOptim" (which can be downloaded from https://github.com/ImageOptim/ImageOptim), with only lossless optimisations enabled, and all .png tools enabled. I’m fairly certain that some of the optimised files have issues which need to be manually corrected, so I’ll probably do that in the next commit.

Note: As I've modified a large amount of files, I have not been able to verify that they are all exactly the same as before, which is why this is a draft PR. Once I’m satisfied with the level of optimisation across all assets, I will work through providing an easy way to verify that all content is the same.

[NeRdTheNed]

(I think the build failing isn’t my fault, it looks like CurseMaven is down.)

[GoryMoon]

You should rebase on the branch again as the cursemaven thing have been fixed