Added Italian locale

The English locale file was a bit vague and I didn't have time to delve deep into the UI source code, so it's a bit generic.
For a better translation:
- What exactly do the "Desktop Video Device" and "Desktop Audio Device" fields refer to?
- Does the `&` symbol in the File menu have a meaning? Is the character next to it just underlined or does it have an hotkey/whatever reference?