Refer to services by their class/interface names, and autowire where possible

Subjectively, everything is good about this. I have discussed with @acbramley just to make sure i'm not misreading anything the emerging practice of autowiring. Loaded everything locally, I can't see any reason not to RTBC this.

The only note is that this technically this is breaking BC - assuming other contrib projects actually use PB services, they would have to update some service references, since we don't add aliases to the old service IDs. I think a clean break is ok on the 2.0 branch.

all cleanup, much more readable and simple. tested manually & automatically, and passing. Shipping it!

Automatically closed - issue fixed for 2 weeks with no activity.