Add and use lift.onDocumentReady function.

jQuery’s just assigns to $(document).ready, while the vanilla
one uses Diego Perini’s contentloaded script to set things
up.
Drop window.liftAjax legacy compatibility layer.
javaScriptSettings returns Box[LiftSession=>JsObj]

We remove autoIncludeJSSettings in favor of an Empty Box
returned from javaScriptSettings; we also fix the
capitalization of javaScriptSettings (it was
javascriptSettings).