Add WebRoot node to project.json on MvcSample.Web
[Fixes #1201] Handle virtual paths in FilePathResult
IServiceProvider.GetService now returns null for missing services

Previously GetService would throw if the requested service was missing.
This commit updates MVC to account for the change in behavior.
Replace calls to GetService<T> with GetRequiredService<T>

Even though GetService<T> still exists, GetRequiredService<T> preserves
the old behavior of throwing for missing services.
Split line made over 120 chars by call to GetRequiredService
Add `DefaultEditorTemplates.MultilineTemplate`
- #965
- test call-throughs from `Html.Editor[For]()` to inner `IHtmlHelper`
 - add another parameter to `DefaultTemplatesUtilities.GetHtmlHelper()`

nit: reorder dictionaries at the top of `TemplateRenderer` slightly
Issue #1206 - DefaultBodyModelValidator throws if get accessor throws.
Fix: The MvcOptions takes in a list of ExcludeFromValidationDelegate (Func<Type,bool>). This func verifies if the type is excluded in validation or not.
Fixing a few comments relating to DefaultBodyModelValidator.
[Fixes #1332] Port IContentNegotiator to WebAPI shim for CoreCLR support

1. Ported IContentNegotiator.
2. Enabled Core CLR configuration
Fix for item #1278 - Add WebAPI ActionResult types and helper methods on
ApiController

Ports all of the WebAPI action result types.
Adding support for bind attribute, does not include prefix property
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