Upgrade to bootstrap 4 and remove bootstrap 4 CDN

[JoepdeJong]

The new login page (#46) is styled with bootstrap for, which is loaded from a CDN. The rest of Connect still uses boostrap 2. If this is updated, bootstrap can be loaded from a local package instead of from a CDN.

• Update Connect to use bootstrap 4
• Remove Bootstrap CDN in

  connect/src/main/webapp/WEB-INF/views/login.jsp

  Line 88 in 3eafcc5

  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.3.1/dist/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">