We have to disable quartz accelerator handling because otherwise
accelerators are performed also from other windows than the main
Geany editor (e.g. Ctrl+V with find dialog open performs the keybinding
Ctrl+V and inserts the text to the editor).

OS X applications have an extra menu entry to the left of the File menu -
an "application menu". This menu usually contains About, Preferences,
Quit. Many users, however, may be used to Geany from other platforms
and expect Preferences to be under the Edit menu so leave them there.
Quit and About are rarely used and the application menu is the place where
they are supposed to be - move these entries from other Geany menus there
and hide them in the affected menus (the quit entry is inserted automatically,
we just need to hide it from File).

Also tell OS X the Help menu is dedicated to help (we get search in
menu entries by name for free thanks to this).

The global menu should refresh automatically based on user actions.
Unfortunately this is not the case when gtk_menu_reorder_child()
is used because it does not emit any signals so the gtk-mac-integration
library doesn't see this call. Refresh the menu manually after calling
this function.