Add 'C', 'M', and 'Q' shortcuts (for all platforms) to parallel 'F5', 'F4', and 'F9'
Add OS X menu for AIS, with target visibility toggle and alarm options

Also abstracted the code which updates the menu item check values into a method so that ti can be called when updating options, as well as at load.
This is necessary in case the AIS options change, and potentially for future options too.
Update shortcuts in context menu, and add Shift-Cmd-Z for undo on OS X

- Changes the right-click menu items to use the new single-letter hotkeys instead of the old F-keys. (Both types of hotkey still work, this only changes the labels.)
- Removes some instances of ifndef __WXOSX___ which needlessly prevented some shortcuts showing on OS X
- Adds a new shortcut for undo, Shift-Cmd-Z, which is the standard on OS X. Both this and Ctrl-Y will now work on all platforms.