Removed methods in Kirby 3.8

[timkinali]

I have not tested but I noticed

$file->panelUrl(true)
and
$file->panelIcon($image)

being used in api.php. I think this should be used instead?

$file->panel->url(true)
and
$file->panel->image($image)

Generally how is the outlook for this plugin with Kirby 4? I think your plugin offers features that is not possible with the K4 native color field so I hope it will be maintained. Thanks for the great work!