A first step to adding automatic dark mode color scheme switching. Adds a new SCSS file at `color_definitions.scss` that serves to output all SCSS color variables as CSS custom properties. And replaces all SCSS color variables with the new CSS custom properties throughout the stylesheets.
This is an alpha feature at this point, can only be enabled via console using the `default_dark_mode_color_scheme_id` site setting.
This adds a site setting (default off) to optionally show a user's local time and timezone in their user card. For example, I live in Brisbane, and if at 3:30PM my time I were to open a user who lives in California's card I would see 22:30 (PST).
Styling based on element-ids, it is impossible for themes/plugins to display multiple cards on a single page. Using classes is a more flexible approach. The element-ids are maintained for backwards compatibility with existing plugins/themes.
