Symbol generation code was copied and adapted from kile.
Use batik toolkit (apache) for svg to png conversion

Requirements:
download compiled batik version (https://xmlgraphics.apache.org/batik/download.html)
Unzip in symbols-ng
Adapt paths in batikConvert.sh

Compile gesymb (qmake symbols-ng.pro; make)

How to use:
Adapt generate-all-symbols.sh (which symbols to generate)
Run "generate-all-symbols.sh"