Angular has been updated to the version 11.

In addition, some minor changes have been done to update the project
and adapt it to some depencencies updates.

Acceptance tests were not working as they wasn't adapted to the Angular
framework after the migration. This commit fixes these test that now
work again.

The user authentication was currently done using a cookie and following
the same style of token as the HTTP Basic authentication (i.e. a
concatenation of user and password joined with a ':' encoded with
base64).

This authentication has been replaced by a standard HTTP Basic
authentication.