`xo` was the only package not to be fixed to an exact version. Fix (hoho) this.

yarn.lock update was long overdue. Some old dependencies were not removed.

The project now provides facilities to launch a standalone selenium server from
the project root.

`yarn.lock` resolved packages with linagora GSO internal proxy registry. This is
not good if someone from outside GSO want to build the project.
Removing it.