[Fixes #429] FileResult

1) Implemented FilePathResult to efficiently return files from disk.
2) Implemented FileStreamResult to return content from a stream.
3) Implemented FileContentResult to return content from a byte array.
@Tratcher I don't think we should be Taking a dependency with StaticFiles in MVC, Can SendFileResponseExtensions be moved to Microsoft.AspNet.Http or Microsoft.AspNet.Http.Extensions? I don't see anything specific to static files that motivates not to do that). @rynowak Any thoughts on this?