SPARQL-level config for iframes

[egonw]

The iframe was also supposed to use the SPARQL-level configuration, but the extracting of the config not yet implemented.

The second commit is esthetic as spaces are removed during config extraction.

Description

The first patch adds the reading for iframe of the SPARQL-level config. Not sure if I never added that, or some patch accidentally removed it. Either way, it needs to be there.

Caveats

None expected.

Check any of the following which apply:

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
  • I have made corresponding changes to the documentation
• This change requires new dependencies (please list)

Testing

The testing is complicated.

• open the web browser console and check in the "Network" tab that the SPARQL queries are made against the right EP.
• check if the matching PR pages show the same content as the following live website pages:
  • https://scholia.toolforge.org/work/Q30149558#cito-incoming
  • https://scholia.toolforge.org/retraction/Q28264479

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have not used code from external sources without attribution
• I have considered accessibility in my implementation
• There are no remaining debug statements (print, console.log, ...)