* Add a postWikitext method and split out postContent
from postHtml
* Move saveSuccess handling into postContent promise
* Connect promise directly to saveComplete instead
* Pass whole response.visualeditoredit object, instead
of splitting into variadic arguments for saveComplete.
* [DEPRECATION] Make serialize return the postHtml promise
and deprecate passing a callback.
Change-Id: I905737515578000b2b87214c92e8b9fe9e82f6b7