Add Garanti Sanal POS Offsite for turkish market

Right now Garanti Sanal POS integration for Shopify is pretty useless, since it is integrated as a direct gateway none of the merchants in Turkey is benefiting from the gateway's important features. Financing options and 3D secure authentication are standards for the turkish market and  Shopify is not being chosen as a provider since these features are not available. If we activate the offsite version, there will not be any problems left.

I guess i made the necessary changes to enable the offsite version