Add new Italian translation

Hey, I just finished to translate everything! :) :+1: 

I did my best to stay conform to the Apple.com website glossary, to find the best way to translate maintaining the meaning and not overflowing the fields spaces (nice UI design though!).


There is only one overflow problem in "_Preferences -> Hotkeys -> Change space + Custom_"

"_Left_" can just be translated with the longer "_Sinistra_".
I could shorten with the abbreviations "_Sx_" ("_Sinistra_" = Left) and "_Dx_" ("_Destra_" = Right), but is not so nice for the UX.

Would be wonderful if some few pixel of width could be added so the the word would not overflow.
Just update me on what you prefer!