use custom folder icon for `icons/classic`

[CWempe]

I noticed the icons/classic folder does not have the custom icon of the icons folder.

Since icons/classic seems to exist by default, I would suggest to use the custom icon for this folder, too.

If you agree I could extend the openhab-icon-theme.json and create a PR.

Like:

    "folderNames": {
        "icons": "_folder_icons",
        "classic": "_folder_icons",

    "folderNamesExpanded": {
        "icons": "_folder_open_icons",
        "classic": "_folder_open_icons",

This would apply for all folders named classic, no matter the parent fodler.. So I don't know if this would be the best solution.

[Confectrician]

Fine for me. :) Let's go, i will assign you.

[CWempe]

Fixed. #207