pass prefixes to org-babel-sparql--current-curies

[VladimirAlexiev]

@johanwk @ljos
ob-sparql.el: org-babel-execute:sparql sets a variable org-babel-sparql--current-curies:

(org-babel-sparql--current-curies (append org-link-abbrev-alist-local org-link-abbrev-alist))

That variable is then used in org-babel-sparql-convert-to-table to shorten URLs returned in query results. org-link-abbrev-alist-local is defined as

Buffer-local version of ‘org-link-abbrev-alist’, which see. The value of this is taken from the LINK keywords.

But in the case of SPARQL there's a more obvious list of CURIEs: the prefixes declared in the query.
So it would be better to extract these prefixes and pass them to org-babel-sparql--current-curies.
They can be extracted as \1, \2 by iterating a regex like this:

prefix:\s*(\w+):\s*<([^ >]+)>

This will work nicely in conjunction with #74