Shipping cost calculated and a few fixes

I consider this a DEV version, since it contains a feature, I did like to have some feedback on.

New feature: Shipping cost calculated for each product with your shipping rules in prestashop!

• Fix rounding issues on all price types. Now we use Prestashop Tools:ps_round
• Multiple fix related to combination/attribute export.

Please give feedback in our forum thread:
https://www.prestashop.com/forums/topic/381026-free-module-google-shopping-flux/