Tweaked the progress indicator a bit.

For one, replaced the fixed-width byte countdown with a simple "% out of [size]". The countdown didn't work out, it was just... odd.

Also made the % adjust the number of shown decimal digits depending on how fast the copying is going.

For fast copies there are no decimals. For slower ones it shows one, for slower yet - two, and for the slowest (like the one on the screenshot) it goes down to 3 decimal places.

The idea, obviously enough, to always show some movement, but try and avoid being too excessive with it.