Add "ID number" column to see your progress

IIRC, the old Gtranslator had the option to show the id number of each string in the leftmost column. I think this is useful when reviewing an already translated file (where untranslated and fuzzy are already at 0), in order to see how far you've got in the review: e.g., if you are at id 300 in a file of 900 strings you know you are at 1/3 of your review.

This should be optional, as normally I prefer not seeing the ID number (it's not useful when translating).