Add the notion of blueshirt-extra to the spec.

This will allow for the addition of access to some user properties
for the blueshirts who will be on the reception desk at the competition.

Change-Id: I86248359db832efbadfb54a72f5549523deca469
Let some blueshirts see (limited) details of all competitors

This changes user detail fetching to using the can_view mechanism
of libnemesis, which has slightly more generous restrictions on who
can see what data. This needed to enable the reception desk at the
competition.

Change-Id: I1a10297b07c7f522d7ca96fe88a5863419154383