[FIX] website: better allow color extensions in the future

addons/website/static/src/js/widgets/theme.js

...te/static/src/scss/options/colors/user_color_palette.scss

...atic/src/scss/options/colors/user_color_palette_body.scss

...ic/src/scss/options/colors/user_color_palette_footer.scss

...atic/src/scss/options/colors/user_color_palette_menu.scss

...atic/src/scss/options/colors/user_color_palette_typo.scss

...tic/src/scss/options/colors/user_theme_color_palette.scss

addons/website/static/src/scss/primary_variables.scss

addons/website/static/src/xml/website.editor.xml

addons/website/views/website_templates.xml