Other: Migrate to Bootstrap 5

[FinnRG]

Split from #6.

Bootstrap 5 beta 3 was released on March 22, 2021 and the stable release is expected to release in the next few months (https://github.com/twbs/release and twbs/bootstrap#31057).

A migration to v5 would make it much easier to increase responsiveness for mobile devices and facilitate the implementation of new frontend features.

[ycanardeau]

@Pyther99 Is there any reason you want to stick with Bootstrap? There are some other frameworks like Material-UI and Primer. Think twice and make some experiments before you start working on this. (I've been spending a lot of time on deciding which of Angular, React and Vue I should use.) Migrating to a new CSS framework is lower priority compared to migration to React anyway. Before creating a pull request, you can (and/or should) do mockups how the user interface would look, and post screenshots here or on Discord. I'll merge the PR if and only if the design looks better than the current one. (I'm quite conservative when it comes to CSS design.)

[FinnRG]

@ycanardeau I would choose Bootstrap 5 as the aim of the migration is not to change the design of the site, this definitely requires intensive testing and consultation on Discord, but to make the site mobile friendly and keep the current design. As VocaDB currently uses Bootstrap 2, this can best be achieved by continuing to use Bootstrap, apart from that it is a well proven framework and I don't really see a good reason to choose another framework. After the React migration, https://github.com/react-bootstrap/react-bootstrap could also be used (which, however, is still based on Bootstrap 4.6).