Warn about using a menu item with wxITEM_CHECK and a bitmap

[KeyWorksRW]

Description:

If a menu item type is set to wxITEM_CHECK and a bitmap is used, the normal checkbox will not be displayed if the item is checked. Instead the bitmap will be shown if checked, and not shown if it is not checked. That might not be what the dev intended, so it would be potentially useful to display a warning about that using our wxInfoBar.

I haven't tested this yet, but I suspect the same problem occurs with wxITEM_RADIO.

[KeyWorksRW]

Need to look into this more -- need to see if this is by design, whether it only happens on Windows, and whether or not wxWidgets documentation covers this.