Prevent re-rendering transactions that don't have read keys

[julienfantin]

A transaction that doesn't have any read keys will cause the entire app to re-render.

While this makes sense as a default, some transactions mutate state that's not rendered and we would like to have some way to override that behavior.

[swannodette]

It's worth considering whether we should have a flag that suppresses re-render from root if the queue is empty.

[anmonteiro]

We used to have ::skip which perhaps we can bring back to serve that purpose.