Tweak catppuccin themes' comment colours and add diff colours

Hello,

I've made some small tweaks to make the Catppuccin themes more in line with the Catppuccin organization's Style Guide. The diff colours now make more sense, with red for a removed line and green for an added line. As well as blue for changed lines. And the comments are a slightly different colour.

One more thing though: when I made the original merge request to add the catppuccin themes, I made it to the master branch, which I now understand to be for KF6. Was/is there any merit to have these on the KF5 branch, since I did not know about the difference when I made my contribution. Or is it perhaps too late now?