-Ystatistics accepts a list of phases for which to print stats

Also cleaned up handling of defaults in MultiChoiceSetting.
Deferring the filter on nays allows the Nil case as at

https://gist.github.com/som-snytt/45b82e58310c8ebb1e5f#file-expander-scala-L29

Fewer things to keep track of on my fingers using rubber bands and bits of twine.