cryptenroll,homectl,journalctl: adjust messages before qrcodes

cryptenroll,homectl,journalctl: adjust messages before qrcodes

Users will generally know what a qrcode is, so let's not treat them as dumb and
explain that it can be scanned. OTOH, we should say what the qrcode contains
and it is useful to give a hint why the users would want to scan it. Reword
messages accordingly.

(Also, don't say "to your phone", when somebody might be using a stolen phone,
or something else then a phone.)