Set default values to match ICES guidelines

[colinpmillar]

Suggested by @iagomosqueira in #25 for the arguments bio.years and sel.years.

If this is done, we should also do it for all arguments, or at least consider which ones would be suitable.

@sarahlmillar - This potentially leads into improving the user freindlyness of the functions' interfaces. And to better user guides specificly for the msy package.