Upgrade to Bootstrap 5

[tomudding]

To make it easier to maintain and extend the website we should upgrade to Bootstrap 5. This will also allow us to do some other things:

• Add a night mode/theme for the website #1004 (previously attempted through main...feature/night-mode)
• Convert tables in admin view to jquery datatables #972
• Info toast for student e-mail address users #1729

I previously tried to do this, see main...tomudding:gewisweb:test/bootstrap-5, however, it took a lot of time to do only a few pages. It also used an alpha version of Bootstrap 5. Hopefully, a new version of Bootstrap (i.e. 5.3) will make this a bit easier.

[tomudding]

I would like to do this per module. However, that will make the website very ugly so I propose the good ol' big bang approach (and potentially some AB testing).