kcms: move desktoptheme and icons kcm to plasma-workspace

They can be useful for mobile, they are taken from the git master of plasma-desktop at 5d8a64ce569b5592d073eaff5f7e8a0c243fc515 sha.

See: https://phabricator.kde.org/T13422

CC: @teams/localization @mart

Please wait for confirmation from localization team before merging it.