Bucketing: Add survival plot to paper

[Chris Warburton]

It shows the shape, i.e. that there are lots of quick finishers and a
heavy tail. This is informative on its own, but also lets us talk about:

 - The height of the tails, as a way of quantifying the effect of size
 - The fact that size 5 seems to be quicker than size 1 (possibly due to
   the effect of a smaller pool of samples?)