Include our new OpenPGP keys in Tails

During the last summit we created at least two other OpenPGP keys for
the project: tails-press@boum.org, and tails-accounting.

At least tails-press@boum.org would be worth adding to the ISO image so
that people have a verified version for free.

Original created by @sajolida on 7655 (Redmine)

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