For pages that can pop back (e.g. Partial pages \ View Components), the
invoking component already creates a new ViewContext. ViewStart, Pages
and Layouts need to share the same Layout. This is required for sharing
ViewData values (such as title).
Fixes#861
RazorView was part of the previous commit but was separated to make it
easier to see the diff in RazorPage that was formerly named RazorView
Adding IRazorPage and changes per code review comments
* Introducing RazorPage and RazorPageOfT that represent the Razor
execution aspect of view execution. Moving view execution hierarchy behavior
(Layout, partial views etc) into a separate RazorView type.
* Renaming IVirtualPathViewFactory to IRazorPageFactory,
IRazorViewActivator to IRazorPageActivator
* Renaming VirtualPathViewFactor to FileBasedPageFactory to
correctly reflect what it does.
Fixes#814
Pranav K