Migrate to Bootstrap 4

[adpi2]

Motivation

Use a more version of Bootstrap to have access to all the new features and improvements.

Identified Obstacles

• There are some breaking changes between Bootstrap 3 and Bootstrap 4.
• We must replace bootstrap-switch and bootstrap-select with the corresponding components in Bootstrap 4.

Implementation Guideline

1. In build.sbt replace "bootstrap-sass" % 3.4.1 with "bootstrap" % 4.6.1 and remove bootstrap-select and bootstrap-switch.
2. Follow the guide in https://designmodo.com/migrate-bootstrap-4/ to fix all the templates in here and all the CSS files in here
3. In the .html template files replace all usage of the <select> element with the Dropdown component in Bootstrap
4. Just removes the 3 lines here which are not needed anymore

Expectations

All pages should render correctly. It should then be possible to migrate to Bootstrap 5 :slightly_smiling_face: