Throw a nicer error when the routing services haven't been added to DI

[DamianEdwards]

Like other parts of the framework we should throw a nice helper exception when services are missing from DI, including the sample call the app needs to add the routing services to DI, e.g.

Routing services have not been registered. Register services by calling 'IServices.UseRouting()'.

[DamianEdwards]

@rynowak @Eilon

[Eilon]

MVC already does this. We can follow the same model.

[rynowak]

Can we not follow the same model instead? It would be nice to do this on Startup instead of on first request

[Eilon]

Hmm ok, do we have an idea of how to do that?

[rynowak]

We can register a marker service and have the routing middleware resolve it when created.

[DamianEdwards]

Ya, the code linked to above does this.

[rynowak]

MVC does it on first request - we should think about changing it to do it when we add AddMvc.

[Eilon]

@javiercn you got that? Let's add this to Routing, and then also change MVC to do the same. I logged aspnet/Mvc#3907 and assigned to you.

[javiercn]

@Eilon will do it for routing and mvc