Create a CA bundle for Tails Upgrader at ISO build time.

This bundle contains both the CA that signed the current certificate,
and the one that will sign the next one.
Announce version 1.2.2
Split to make this section easier to apprehend
People on DVD will receive errors from Tails Upgrader
Tell everybody to upgrade
Fix link
Patch tails-iuk to use the correct website certificate.

See commit fbd5a82.
Merge branch 'bugfix/handle-website-CA-change' into stable
Update website PO files.
Merge remote-tracking branch 'origin/master' into stable
Update version and date for 1.2.2.
Update changelog for 1.2.2.
Update upgrade-description files.
releasing version 1.2.2
Phrasing improvement in the Changelog.
Indicate that users *can* skip 1.2.2.
A manual upgrade is required for 1.2.2.
Make the change more about "upgrade checking".

Especially since we don't provide an incremental upgrade.
Simplify announcement for 1.2.2

All users will have to do a manual upgraed, either to 1.2.2 or to 1.2.3.
So let's encourage them to do it for 1.2.2: this will save them error
messages after January 3rd and save us some user support.
Adjust date