Web.config/ViewStart replacement - IUsingsProvider, Layout discovery

[NTaylorMullen]

e.g. Need a way to specify the list of usings for the RazorViewPage.

Figure out how layout pages are specified and discovered.

e.g.
@layout directive

ViewStart pages or ViewStart page replacement.

| 94 | 10190 | Reported By: Pranav K |

[pranavkm]

#774 tracks the notion of IUsingsProvider.