Add support images attribute

[devmansurov]

Hello! As far as I know, now you can add a picture only for the main product variant. Therefore, I propose to make a field for loading images as an attribute so that later we can reuse it everywhere (e.g on each product variants)

[glennjacobs]

I think an attribute field type of "image(s)" is inevitable. However, our focus right now is finishing off the core.