* Update brand logo color (WIP)
Need more SVG hackery for proper transparency...
* Add SVG favicon (WIP)
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* Create transparent logo variant; use for brand icon
* Update primary color for all logo assets
* Add small white stroke to favicon
* Switch to SVG favicon
* No change if unsupported
* If supported, still auto-refresh at the selected frequency (if any),
but only if not hidden.
This is useful for always-on displays (e.g. a "baby clock"). Fixes#253