OS X menus and menu items

Most of these already work in this commit, but not all.
Some need some more complicated handlers, for which I will make a separate commit for clarity.
Many of the simple ones use the existing handlers for the toolbar buttons, though I have also added several new simple handlers here.

I have extended the SetToolbarItemState function to also set the state of the corresponding menu item, and have used it extensively to replace existing places where the toolbar item state was previously set manually.
OS X menu handlers for mark, route, and measure items

These involved wrapping some of the existing code in chcanv.cpp in function wrappers so I could call it from chart1.cpp.
OS X menu handler for Help menu item

I moved the code to load the external help from about.cpp to chart1.cpp so it is globally available, and I call it from the chart1.cpp menus and also from the original location in about.cpp