upgrades: Initial user experience

At the hackathon, I sat next to a beginner user as he set up a VM with the stable virtualbox image. We observed the following:

• apt cache is not updated right away, even when clicking the manual update button. It only updated with the apt daily timer.
• backports is not enabled right away, until the freedombox-setup-repositories timer runs.

Proposals:

• Manual update should allow updating freedombox package (#1638 (closed)).
• Manual update should also update the apt cache.
• When manual update is run, consider performing all of the steps under "Manual Updates from Terminal" on https://wiki.debian.org/FreedomBox/Manual/Upgrades to fix common problems.
  • APT::Fix-Broken option may help.
• Enable backports during initial setup.
• Consider running an update during initial setup.