needed: various PM boxes status indication on inbox page

[emuler]

Most of us only visit our inbox when using the PM service. On that page, the status of how full the inbox is is displayed prominently. However, the status of the other boxes is not known unless we visit each box in turn. I just found that my sent box was 94% full. Had to do some urgent housecleaning. Perhaps an indication on the inbox page itself of how full the other boxes are would be useful to all. Doesn't need to be fancy; just the % value will do.

btw. what happens when the sent box gets full?