Fix mutable publish/retrieve timing status displays. Fixes #1505.

Fix mutable publish/retrieve timing status displays. Fixes #1505.

publish:
* encrypt and encode times are cumulative, not just current-segment

retrieve:
* same for decrypt and decode times
* update "current status" to include segment number
* set status to Finished/Failed when download is complete
* set progress to 1.0 when complete

More improvements to consider:
* progress is currently 0% or 100%: should calculate how many segments are
  involved (remembering retrieve can be less than the whole file) and set it
  to a fraction
* "fetch" time is fuzzy: what we want is to know how much of the delay is not
  our own fault, but since we do decode/decrypt work while waiting for more
  shares, it's not straightforward