Display ISNI according to ISNI standard

MOD 11-2 is defined in ISO/IEC 7064 and there's code available in a PyPI package https://pypi.org/project/python-stdnum/

As an aside, the draft of the ISNI standard, ISO/IEC 27729, that I found has the following about rendering:

> When an ISNI is written, printed or otherwise presented in a human-readable format:
> a) it shall be preceded by the letters ISNI, separated from the identifier by a space, and
> b) the 16 digits shall be displayed as four blocks of four digits, with each block separated from the next
> by a space.
> EXAMPLE ISNI 1422 4586 3573 0476

OpenLibrary isn't currently following these rendering rules.

_Originally posted by @tfmorris in https://github.com/internetarchive/openlibrary/issues/6841#issuecomment-1208348204_