Wiped out all GList instances, except in libcroco and libnrtype.
Wiped out all GSList instances
Fixes like a hundred memory leaks.
 and 2 occurrences in sp-style-elem.cpp tied to libcroco
 and 1 occurrence in widgets/font-selector.cpp tied to libnrtype
 except where it introduced a crash: tentative diff was https://gitlab.com/marcjeanmougin/inkscape/snippets/1677547 but crashes. This is probably because our code for actions is too unconventional and bad enough in gtk, and gtkmm fails some casts :/