Moved View/Negotiate to INancyModule

Superseeds PR #1472

Add's missing XML Comment and moves View/Negotiate to the `INancyModule`

This allows the module to be mocked for use in 3rd party app testing.

i.e in SimpleAuthentication library we have an `IAuthenticationProviderCallback` class which has the module passed into, however this cannot be tested without attempting to mock the entire NancyModule. 
I'll pull ViewRenderer out of the module, I concur with you, the ViewRenderer is its own implementation and doesn't actually belong inside the Module IMO. Nor should it dictate how the Module is written. 

ViewRenderer should also have an interface. 

I will update this.