make `gps ls` work when in middle of rebase

[drewdeponte]

The ideal would be that when we are in the middle of a rebase of the patch stack we can still run gps ls and see the current state of which patches have been played already, where we are stopped at, and which patches are to be played still.

Not sure exactly what this would look like visually.

Maybe just the patch stack with some ------ line indicating where it is stopped at with the patches to be played above it or something.