Feature Request: queue size

Hi,

I have been using Klibido for some time because of the too high memory
requirements of Pan v0.14.

I'm now using Pan again thanks to the great work made on the new beta
versions, but there's a little feature I'm missing from Klibido. The
latter displays the queue size in the queue manager, and I don't find
this information in Pan.

Could something like that be added to Pan? Based on this, an ETA could
also be computed (i.e. to reach an empty queue).