Currently, if firewalld is not running, then the firewall zone combo is
always insensitive. This would make sense if firewalld was great and we
were to consider it a distro bug to not have firewalld running and
enabled, then users would be able to see the option is disabled and
think "maybe my distro has done something wrong."
But in actuality, firewalld is not really great, only Fedora ships it
and we're not really recommending it to other distros. So hide the combo
if it's not running, else it's just broken on $NOTFEDORA.
https://bugzilla.gnome.org/show_bug.cgi?id=763477
The previous code would stop validating when an error occurred which
meant that when a page contained multiple errors, only the first one(s)
to be checked would appear in red.
Now, all the errors will appear in red.
https://bugzilla.gnome.org/show_bug.cgi?id=734472
When a configuration setting is wrong, set the entry or file chooser
that contains the incorrect information to be surrounded by red.
This makes it easier for users to find where the error was made that
disallows them to click the "Apply" button.
https://bugzilla.gnome.org/show_bug.cgi?id=734446
