Support Dark Mode

[codedread]

1. Update Extension icon so it looks better in Dark mode
2. Update Popup window for dark mode (see prefers-color-scheme)
3. Update Spaces Quick switcher window for dark mode
4. Update Spaces window for dark mode

[codedread]

Prelim research so far for Extension icons:

• The standard plan seems to be to implement the icon_variants proposal
• Chromium bug, tried but does not seem implemented yet?
• Webkit bug, may be implemented?
• Firefox bug
• It seems like Firefox might support this in some way via the theme_icons property, but it's non-standard.

I filed enhancement (issue #27) for this extension to support Edge, Firefox, Safari browsers too...

[codedread]

A Chromium magician once told me:

Run canary chrome from command line with --enable-features=ExtensionIconVariants

[codedread]

https://source.chromium.org/chromium/chromium/src/+/main:extensions/common/api/_manifest_features.json;drc=ad93938196619ea0a14fcd1e2aef3bc712e2cc3e;l=287