Slitherine

Just a minor bug on the brand new skins, while I have not tested every single faction, there are multiple vehicles that do not accept any skins, many being soviet tanks older than 1941 models, like BT tanks and M1939 T-26 tanks. Artillery seems to fine, but I have not extensively checked every single piece. Might be more bugs for all other campaigns.

Thx for reporting. LL and captured are not included per se yet, but standard Sov ground should work, so we fix these asap.