InfoBox: GTK4 prep, code style

[danirabbit]

Review with hide whitespace

• Inline namespace
• bump copyright header
• Use Granite.HeaderLabel
• Lay out vertically
• Make sure ipv6 addresses use their own labels

BEFORE

AFTER

[danirabbit]

Yeah an unfortunate stylesheet quirk that can't really be fixed here. This can wait until after the GTK 4 branch lands if it's too bothersome

[jeremypw]

OK, as this is a significant diff and the port is not too far away let's merge.