Add modus operandi themes

[amousset]

This PR adds themes based on the light variants of the carefully designed modus themes (built-in with Emacs). This is not a port of the original theme, as Emacs themes are much more than a color scheme, but a set of Helix themes inspired by the defaults of the modus operandi (light) theme, and reusing their color palette. They follow the same goals, i.e. legibility and accessibility (following the highest WCAG AAA standard), even over esthetics when necessary.

The themes are:

• modus_operandi: the base theme
• modus_operandi_tritanopia: a variant of the base theme for blue-yellow color deficiency
• modus_operandi_deuteranopia: a variant of the base theme for red-green color deficiency
• modus_operandi_tinted: a variant with a toned-downed background

modus operandi

modus operandi tinted

Licensing note: Even if the theme for Emacs is licensed under GPLv3+, the color palette itself is placed under CC0.

[zetashift]

Not a maintainer, but a modus fan! This is really cool, thank you for this :D

[aboe76]

@amousset will you try to add the 'modus-vivendi' variants as well?

[atahrijouti]

@amousset and https://protesilaos.com/emacs/ef-themes too please :-)

[matoous]

@aboe76 here's a draft, you can give it a try: #8894

[amousset]

I don't plan to work on additional modus themes for now (but it seems @matoous does 👍 )

[aboe76]

@aboe76 here's a draft, you can give it a try: #8894

Yes thank you @matoous, just compiled your PR and it works nicely