View as web page fix

Hey Guys,

I ran into an issue including the view as webpage functionality at the top of our API-generated newsletter.

From looking at a couple posts on your forums of the XML you expected, analogs to "view_as_web_page_link" never showed up but "view_as_web_page_link_text" did. Sure enough, changing the "view_as_web_page_link" -> "view_as_web_page_link_text" in my json request payload allowed my emails to be created as intended.

I have updated the DataMember serialization decoration and changed the property name for consistency in your wrapper. Hoping this fix saves another pour soul 4 hours of debugging and guess work!

-AP