This ports back the following commits about lossless PNG-shrinking:
0.4.15-dev-6410-g cf4bb8fced [WALLPAPERS] Optimize PNG images (#5506)
0.4.15-dev-6398-g e5993f13f0 [REACTOS] Optimize PNG images (#5492)
0.4.15-dev-6376-g 8f3a09722e [MSPAINT] Optimize images for help docs (#5486)
Most of those PNGs have not been touched ever since we switched from SVN to git, so they can safely be ported back by copying over.
Only the Mizu-wallpapers had something specific to take care about:
They were added (still with a different name) by 0.4.12-dev-819-g 181a2b3359 [WALLPAPER] Add ReactOS Soft Blue
Later they were renamed by 0.4.14-dev-1435-g 6a8c894642 [WALLPAPER] Rename Soft Blue to Mizu (#1945)
and with that commit a fourth pic was added for Mizu.
Since they are only copied to iso but are not explicitly referenced by the theme, I decided
to port back the renaming part (without adding the fourth pic) to releases/0.4.12 and 0.4.13 to harmonize their name everywhere.
But did not port them back any further than where they existed already.
Tweak a few related txt/md/html files also with trivial stuff like EOL-whitespace-removal.
0bd16f5756