Introducing RazorViewFactory for RazorView for https://github.com/aspnet/mvc/issues/1506

1. Adding IRazorViewFactory and RazorViewFactory
2. Removing IRazorView
3. Updating MvcServices and RazorViewEngine

@pranavkm  please review this PR. 
`CreateViewEngine` creates a `IRazorViewFactory` by default which should handle this for you (if it isn't already). It'll  make these tests less verbose.