Removed ProductVersion fields from cart fixtures, as it shouldn't be there.
Added discount submodule suggestion to composer.json.
Removed old composer silverstripe-payment config.
Added default product image
ProductImageTest now uses shop.yml fixture
Merge pull request #242 from markguinn/feature-default-image

Added default product image
Minor tidy
API: changed ShoppingCart add and setQuantity functions to return the new/existing item, rather than returning true.
Merge remote-tracking branch 'upstream/master' into ss3
this is the first mearge into SS3
Edited the ShopDevelopmentAdmin page with more instructions