Refactoring ServiceCollection

* Remove use of IConfiguration from ServiceCollection
* Removing the Add* methods from IServiceCollection that don't accept an
  IServiceDescriptor

Fixes #116 #117
The only use case for passing `IConfiguration` into `ServiceCollection` is to be able to replace registered services with types specified from config - https://github.com/aspnet/DependencyInjection/blob/dev/src/Microsoft.Framework.DependencyInjection/ServiceDescriber.cs#L125-L133. We don't use this feature in Mvc's functional tests.