Edit shopping cart item functionality does not pre-set correct picture

[AndreiMaz]

If you click on the "edit" buttton, then all product attributes are pre-selected (as per shopping cart item). We should also pre-set the main picture if some of the selected attributes has custom picture.

The same happens when some attribute is pre-selected and this product details page is open (even not "edit" mode)

The issue is that there could multiple (distinct) attributes that change pictures. For example, attribute 1 with some value has one picture. But attribute 2 with some value has other one. Imagine that both of them are pre-selected. Which picture should we display? Maybe, the one of an attribute with higher display order?

Or we can load pictures using AJAX (the same as it's done for dynamic price update). Anyway we're going to introduce pictures per attributes soon - #290 (most probably)