Menu shortcuts on mac.

[Lord-Kamina]

By making some small changes to the gtkosxapplication import code (will eventually send a PR when I've actually got things working satisfactorily) I was able to get it working but I notice MANY shortcuts are set as their Linux versions (shortcuts that work correctly in the 1.3 app bundle). From reading up I saw references to the accel_map template files; along with a suggestion to use the save function to get an actual template I should then edit. I tried so but got an empty template file; so I'm not sure if maybe I should call this function on an instance of some object or whether I'm just barking at the wrong tree in how to fix this. Suggestions?