Incoming content negotiation based on content-type

[pranavkm]

Right now individual formatters look at a list of content types and decide if they support the request. We need to figure out what a proper pattern for this needs to be.

[harshgMSFT]

Workitems:

1. Provide a collection of Input formatters: The defaults will be exposed through MVCOptions.XmlInputFormatter should be chosen based on MvcOptions. #851 -1 day.
2. Changing the current api structure to use the httpabstraction header parsing and use that for content type matching. - 1 day.
3. Need to design around how to return an exception back. Content Negotiation need to return 400 Bad Request \ 415 unsupported media type  #458 - 3 days

   Where do the input formatters hang off ( it is helpful if someone wants to use a filter to add/overide the default formatters).