Wrap normalize ProductLookup.load_product_batch response logic into a method

* Amazon API returns a Hash when only one product is returned and an Array if more products are returned
Ignore and remove malformed products from load_product_batch response

* Treat exception when trying to access needed product attributes of the response on get_attribute_hash and returned nil when some exception happens
* Call .compact in response to remove nil products (see above)
Allow products without similarities to be on the database

* Refactor get_ten_asins signature to allow page, brand and keywords param