Handle items without images

Some (a lot actually) items do not have images on bol.com and the data retrieved from the API does not contain the images array, making the call fail... There must be better way to systematically check for non null arrays before looping on it  and risking failure but for now, this is how I solved it...
Clean up whitespace
Tests: added incomplete product test (#6)
Wrap cleanProduct() bits in try...catch (#6)
Tests: fixed incomplete product condition (#6)