starting to hide references to IFormatter
eliminated the old JsonMessage marker interface and convention.  Closes GH-627
more work to decouple from IFormatter
removed the conditional behavior.  Closes GH-628
added the IFubuRequestContext hub service
OutputBehavior is now using the IFubuRequestContext
the IConditional's and IMediaWriter's are mostly using the new context
XmlFormatter is now stateless.  Duh.
introduced the temporary JsonSerializer.
made the json serializers be IFormatters, OutputNode.Add() methods
made ModelBindingReader stateless
added InputNOde.Add()