Adding native parameters: body2, rating, privacyLink

[aneuway2]

Type of change

• Feature
• Does this change affect user-facing APIs or examples documented on http://prebid.org?

Description of change

Adds support for body2 rating, and privacyLink to prebid.js and the AppNexus adaptor.

• Example implementation

var adUnits = [{
  code: 'div-id',
  mediaTypes: {
	  native: {
		  body2: {
			  required: true
		  },
		  rating: {
			  required: true
		  },
		  privacyLink: {
			  required: false
		  }
	  }
  },
  bids: [...]
}];