Draft: Configure and optimise mathjax for SVG and speed
Deleted extra_markdown.tpl, nbconvert_fix.py, execute.py, theme/main.html, src/scripts/thebelab-custom.js, src/scripts/thebelabhelper.js
Deleted extra_markdown.tpl, nbconvert_fix.py, execute.py, theme/main.html, src/scripts/thebelab-custom.js, src/scripts/thebelabhelper.js