Display the Tails version number during boot (Boot Loader Menu or Welcome Screen)

When using Tails for a while you can end up with different Tails USB sticks with different versions. It would be nice to be able to tell the version immediately on the main screen when booting, to know if you are running a new version.

This will also confirm your update if you are rebooting after an update.

The downside of the proposal is that the screenshots about the greeter will get more quickly outdated.

This was also raised as an issue during broken upgrades. A user didn't manage to perform https://tails.boum.org/news/version_4.14/broken_upgrades/ and didn't know how to check which version they were running. Removing P:Low and adding C:Upgrader.