show calculated size incrementally in the info pane

[cyberduck]

17c06b5 created the issue

When the user selects "Info" on a directory, the info pane allows to compute the "contained" size by recursively stat-ing the size of all contained files.
On directories with lots of files this can take a really long time. It would be extremely helpful to show the computed size incrementally instead of waiting until the final number is computed. This gives a quick "lower bound", that is useful in many occasions.

[cyberduck]

@dkocher commented

In 1540f0c.