Show progress when working on a very large message?

[eyalroz]

Sometimes, we need to perform charset and/or direction detection on a very large message; and this can take a bit of time, especially when running on old, slower, hardware. While this is relatively rare, perhaps we should bother to identify when we have a lot of work ahead of us, and have some kind of progress reporting, or show the meteors, at the bottom of the window.