Fix for #1277 - Add Options/Startup API for WebAPI shim

Adds an options class, as well as a default options setup that will
configure the default set of formatters.

Currently most of what options needs to do is a placeholder, but it later
do things like add ApplicationModelConventions, filters, formatters, model
binders, etc. Those will be added in follow up items.
Fix #1276 - Implement WebAPI action conventions and overloading

This change adds ApplicationModel conventions that can enable WebAPI
action conventions (verb mapping) and WebAPI overloading.

The conventions activate when a controller has a marker attribute.
ApiController has this attribute, so any ported code will automatically
opt-in.

Also ported some old tests for action selection to our new functional test
framework.
Fix for issue #1279 - Add .Request property to ApiController

This change adds a .Request property to the ApiController class that can
be used to access an HttpRequestMessage wrapping the HttpContext.

The HttpRequestMessage is stored in an http feature to make it accessible
to model binders and other infrastructure.
Fix for issue #1281 - Add ModelBinder for HttpRequestMessage

This change adds a ModelBinder that can bind an HttpRequestMessage to an
action parameter.

This builds on an earlier change to construct and store the request
message in the HttpContext via an http feature.
Fix issue #1280 - Add HttpResponseMessageFormatter

Adds a formatter that can convert an HttpResponseMessage returned from an
action into HttpContext.Response output.