Disable IRegistration for Unit Tests

This add's a new setting to the configurable bootstrapped which filters out non-nancy implementations of `IRegistration` (formally `IApplicationRegistration`)

This means dependencies registered via the interfaces won't be loaded up during tests.

```csharp
var bootstrapper = new ConfigurableBootstrapper(config =>
{
    config.DisableAutoRegistrations();
    config.Module<NoAppStartupsModule>();
    config.Dependency<INoAppStartupsTestDependency>(typeof(AutoDependency));
});
```

Reason: If you're registering something like RavenDB store, and you have the connection string in the Web.Config file, but in your unit tests you're using RavenDB.Embedded, then it will throw since the RavenDB dependencies are not there, and the config setting is not there.

Turning this on will allow you to register your own dependency for RavenDB store without conflicting with the implementation used in your website.
I think this belongs in Nancy.Testing.Tests alongside e.g. ``ConfigurableBootstrapperFixture``.