Adjust ProductRequestHandler and add support for platform-specific Attribute names

Recently, we tested exporting products to Merchantry. During testing, we identified missing, extraneous, and improperly named fields. 

### Changes

**For Merchantry, I did the following**
* Removed instances of 'lang'='en-us'.
* Removed Locale.
* Added a type attribute to Images. First image is 'Main' and subsequent images are 'P1', 'P2', etc.
* Relocated Relations (this section needs to come before Attributes).
* Moved CategoryID to the top of Attributes.

**For LivingSocial**
* Renamed most Attribute fields.
* Added some LS-specific required Attribute fields (Link and Shipper Responsibility). 
* Added required category-specific Attributes with 'N/A' string value. 

### RFC

This PR replaces Merchantry's Attribute names with LivingSocial's names for the same Attributes. For example, Merchantry calls product weight "ShippingWeight" while LivingSocial expects "SKU Weight (Number)" and Merchantry calls product name "Title" while LivingSocial expects "SKU Name". 

Merchantry is used by more than one platform. We need to come up with a way to support attribute name overrides elegantly.