ISBN pattern needs to be updated

[UlrikeS91]

I just noticed that our regex pattern for ISBNs is not inclusive enough. For example, the Paxinos Rat Atlas 6th edition's ISBN is 0-12-547612-4.

If I'm not mistaken, our pattern (^([0-9]{3}-|)[0-9]{1}-[0-9]{3}-[0-9]{5}-[0-9]{1}$) enforces a (3 digits -) 1 digit - 3 digits - 5 digits - 1 digit pattern (i.e., X-XXX-XXXXX-X (10-digit ISBN) or XXX-X-XXX-XXXXX-X (13-digit ISBN)), but the ISBN above follows a 1 digit - 2 digits - 6 digits - 1 digit pattern.

I'm not 100% comfortable with proposing any changes to the regex (because it's a regex...). Could somebody fix this? @Raphael-Gazzotti maybe?

I'm not sure if this also affects ISSNs, but we should probably investigate.

FYI @lzehl