Use thin space as digit grouping separator

[KenKundert]

Change digit grouping separator from a full space to a thin space.

Use of a thin space over a full space is an emerging standard (https://en.wikipedia.org/wiki/Decimal_separator).

I personally find the full space jarring in that it seems like I am looking at two separate numbers rather than one long number. As a result I have to concentrate to use Wasabi in order to make sure I do not misinterpret the numbers.

[yahiheb]

Related to #2588

[editwentyone]

please see also #2588 (comment)