Most of the PNG/JPG/GIF icons in the pix folder are redundant if an SVG
file is available, so they have been removed to simplify maintenance.
This commit removes all redundant icons from the pix/ folder. Additional
redundant icons in the icons/ folder will be addressed separately while
reviewing the FontAwesome icons and their SVG versions.
The absence of SVG files has been addressed by including them,
sourced from the respective FontAwesome versions available for
download at https://fontawesome.com/icons
