Merge the current runner state into a new actual running state api

[philwinder]

The "activeInstances" api is powered by the runner's activeModelInstances. This is the old definition of things that are running.

I kept this for the time being because it has useful information in there like GPU usage and such. Also backwards compatability. But in reality it has nothing to do with the slots that have actually been scheduled. It's not part of the slots code.

So we need to merge the idea of runner slots and activeInstances together into one unified thing.