applets/256: Add dark version of analogclock

Now that the analog clock applet adapts to colorscheme (https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/547), let's also add a dark version icon to match it on the applet selector.

Adds colorscheme css support also to the light version so both versions are kept in sync.

icons	icons-dark

Note to test without getting crazy: it will require a clean-build to install the new icon and not the light fallback