Poor integration of dependencies

[loic-yvonnet]

The integration of Bootstrap and KaTeX is fairly poor: these dependencies are copied/pasted without using a package manager.
Initially, a CDN was used but then, we faced a cross-origin problem in some IT context. The quick and dirty fix consisted in copying locally the content of the CDN.
The actual fix involves the clean integration of Sass, Bootstrap and KaTeX through npm.