Added internationalization support and Italian translation for the Mac OS X version

Added internationalization support using gettext and Italian translation for the Mac OS X version.
There are some stock buttons that are not translatable yet (like Forward and Go Back buttons) because their text is probably part of the Qt library. I've already read something around the web and it seems to be easy to solve because Qt also includes translations for stock buttons, I just have to figure out how to activate them. There are also some per-language adjustments to be made to few of the translated texts since in some cases they exceed the length of the english counter parts resulting in an overflow.

Please, tell me what you think.

Thanks
CB