Separate document and document view stores

I think it would be nice if the current DocumentStore would be split in:

1. DocumentStore, containing just the open document.
2. DocumentViewStore, containing view state for the open document (currently only focus, but in the future viewport, zoom, etc).

Let's ignore undo/redo here.

I tried this, but didn't succeed because of the following.

Issue: auto-focus on added member

After adding a member, focus should be on that member. I would imagine that both stores listen for ADD_MEMBER actions and DocumentViewStore could gently wait for the member to be created using waitFor([DocumentStore]) before setting the focus. However, DocumentViewStore has no way of knowing the key of the added member.

I don't think it's a good thing to trigger some SET_FOCUS action from the DocumentStore after adding the member (perhaps it's not even possible with our dispatcher). Workaround would be to keep a lastAddedMember key in DocumentStore for the DocumentViewStore to read, but that doesn't feel right.