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
This code is fairly independent of the rest, and we don't want
net-device-wifi.c to become too massive and unmaintainable.
The code in connection-editor/ is fairly similar to
nm-connection-editor, with some simplification because we
currently only edit wireless connections.
The code in wireless-security/ is almost a straight copy
of the same code in nm-connection-editor, with some changes
to the .ui files to make them fit better in the new design.
