Fix or remove bad links

Started having a look at external links, and found some that lead to unexpected domains, so let's fix them.

• Changed Libre Graphics World to Libre Arts, unclear where the old page leads now. https://librearts.org/2021/01/introducing-libre-arts/
• Some SVG files had a link to a Sodipodi web page, but that address now leads to an Indian adult toy page (!). Here I just removed the link since Sodipodi seems to be superseded by Inkscape many years ago, but can also replace it with https://sourceforge.net/projects/sodipodi/ if you prefer.