React to Options changes

FYI the file is spelled wrong: SignalRServiceColletion
With this and the Configure methods we allow two different patterns:

``` C#
// Option #1
services.AddSignalR(configuration, opt => { ... });
// Option #2
services.AddSignalR(configuration).Configure(opt => { ... });
```
I am not sure we need both. The latter may look a bit nicer at first glance but it is a bit weird because although the AddSignalR and the Configure methods are both applying changes to the configuration, only one of them is called "Configure". We could even consider doing this although it looks more verbose:
``` C#
// Option #3
services.AddSignalR().Configure(configuration).Configure(opt => { ... });
```
I would really want to hear what folks think because we should be applying a consistent pattern across frameworks.