Support image and imageList item property types

Use new recommendation endpoints

Added parameters amount,price,profit to AddPurchase and amount,price …

…to AddCartAddition

Added support for view portions

Support returnProperties and includedProperties parameters of ListIte…

…ms and ListUsers. Send User-Agent HTTP header. Use POST for recomm requests.

Added support for using a proxy server

Node.js client for Recombee recommendation API