Mac menus

As per the discussion on the forum, I have continued the Mac menu bar work I began in pull request #171.

The arrangement of the menus, and what is in them, is not necessarily final. (I keep thinking of new things to add!)
I would like feedback and input on this. What do people think should be here? Are the names of the menus I have created (Navigate, View, Tools) good, or should they be different? Should some of the items be in different menus?

I have rebased this onto today's beta, and made it into four commits to make it a bit clearer what I did. Each has a hopefully-informative commit comment...