Found during the course of investigating #607. Right now we attempt to create the UI of the Pane immediately on construction. While investigating commandline args, I'd try to create a bunch of Panes. This didn't work, because the Pane would have 0 height/width, and would fail to create the UI, or attache the child, until a resize came through.

This is overall bad. We should probably wait until we complete the first layout to calculate how much size we have. Part of the reason this was so bad is that we're manually setting the width/height of our rows/columns to the number of pixels equal to some % of what's available. When that's being calculated, there's only 0px available.