Mark all remaining translatable strings

[stefwalter]

We should mark all remaining translatable strings. In particular:

• Strings in code should be marked with _("String")
• Strings in HTML should be marked with the attribute translatable="yes" in their surrounding tag.
• Numbered translatable strings will need to use cockpit.ngettext("Singular", "Plural", count), likely wrapped in a cockpit.format(...) call.

This will require a bit of refactoring in places:

• Where we don't have a translatable string alone in a tag, it probably needs to be put in its own tag, and then checked that this doesn't break things.
• In cases where we use Mustache we need to add translatable="yes" attributes, and then run cockpit.translate on the resulting element.
• In cases where we don't yet call cockpit.translate() on a page, we need to do that.