Backport formatting from Julia course (2022-06-08)

Mainly code highlights, uncluttering and pictures.

@laurent.heirendt is there a place to document the use of .leader and the emoji for theme users?

Refs to what this looks like:

• https://courses.lcsb.uni.lu/2022-06-08_JuliaForNewcomers/latest/#/4
• https://courses.lcsb.uni.lu/2022-06-08_JuliaForNewcomers/latest/#/5