Say an update is running before it starts, not only after

Asked what happens if someone shuts the laptop down mid-update, the honest
answer turned out to be poor. The inhibitor does stop them - logind refuses and
falls back to org.freedesktop.login1.power-off-ignore-inhibit, which is
auth_admin_keep - so the desktop answers with an administrator password prompt
reading "Power off the system while an application is inhibiting this". systemd
ships that string untranslated, it never mentions updates, and no KDE catalog
contains any shutdown-blocked text at all. Only systemctl names the reason.

So a notification now goes out before the transaction, asking for the machine to
be left on. Notifications gained a tag: the result replaces the start message in
place rather than stacking a second, contradictory bubble beside it.

Tagged notifications also carry a queue flag. "An update is starting" is only
meaningful while somebody is looking, so unlike the result it is not spooled for
delivery at next login.

po/de.po

@@ -264,3 +264,10 @@ msgstr "Abgebrochenes Update wird beendet"
 
 msgid "The last update was cut short, most likely because the machine was switched off. It is being finished now."
 msgstr "Das letzte Update wurde unterbrochen, vermutlich weil der Rechner ausgeschaltet wurde. Es wird jetzt zu Ende geführt."
+
+msgid "Installing updates"
+msgstr "Updates werden installiert"
+
+#, c-format
+msgid "%d packages are being updated. Please leave the computer switched on until this is done."
+msgstr "%d Pakete werden gerade aktualisiert. Bitte den Rechner so lange eingeschaltet lassen."