Bug: MacOS Menu

[rgleason]

See Manfred's post #1507

For MacOS there are two options:
- simple fix: when activating weatherfax, not only open the Weatherfax window, but also make it the "active window" thus change the menu ...Against the rules (to change the menu), but it will work and should be apparent to the user
- legal fix, if there is need for context dependent menu entries, then "add an extra menu entry (e.g. weatherfax) to the existing menu bar" , but leaving the other entries in the standard OpenCPN menu there. In that new menu entry, we could find the retrieve points, ...