build with nested forms

@item.item_item_properties.item_property_id is wrong, @item.item_item_properties is a collection, use [iip.object.item_property.name](http://iip.object.item_property.name) and iip.object.item_property_id instead.

imagine @item.item_item_properties is something like an array [item_item_property1, item_item_property2], you can’t call item_property_id on an array, you have to call it on one of the items inside it, and that “iip” variable, if you call .object on it you get that item from within the array.

check out the cocoon gem, it made nested forms really simple.