Generate png and pdf from svg

[plessbd]

instead of using chromium to generate both the svg and png, this has it just generate the svg and then uses rsvg-convert to create both the png and the pdf and adds the exif data for both png and pdf

This also combines the two commands rsvg-convert and exiftool to be run in one proc_open

[jpwhite4]

Need to update the documentation for the new dependency on exiftool and dropping ghostscript.

grep -w ghostscript -R docs
docs/software-requirements.md:                  ghostscript php-mbstring php-pecl-apcu jq \

also you are missing the perl-Efittool infor from the Centos 7 section in the same file.

[jpwhite4]

Don't forget to update the pull request title and turn it into a proper sentence for the changelog. Also need to add the appropraite labels and milestone tags.