Update missing body ID prediction to handle, say, the Maraquan Mynci.

It turns out that some pets for seemingly nonstandard colors have the
standard body type anyway, and vice-versa. This implies that we should
stop relying on a color's standardness, but, for the time being, we've
just revised the prediction model:

Old model:
    * If I see a body_id, I find the corresponding color_ids, and it's wearable
      by all pet types with those color_ids.

New model:
    * If I see a body_id,
        * If it also belongs to a basic pet type, it's a standard body ID.
            * It therefore fits all pet types of standard color (if there's
              more than one body ID modeled already). (Not really,
              because of weird exceptions like Orange Chia. Should that be
              standard or not?)
        * If it doesn't also belong to a basic pet type, it's a nonstandard
          body ID.
            * It therefore only belongs to one color, and therefore the item
              fits all pet types of the same color.
reload pet thumbnail when and only when its appearance changes