Make OrchardStarter modify static configuration in an optional way

[orchardbot]

@Piedone created:
https://orchard.codeplex.com/workitem/20919

Currently OrchardStarter modifies static configuration classes, like the Web API-related GlobalConfiguration and MVC statics (ControllerBuilder, FilterProviders, ViewEngines, ModelValidatorProviders). It would be better if such static configuration would be optional (i.e. the caller could opt with it or not) or even better, if web initialization code would go into a separate initialization logic, like WebStarter.

Admittedly this is only an issue if you want to use Orchard not as a standalone web app but as part of another app, with Orchard App Host..