editor: fix enabling the Apply button for EAP-PEAP and EAP-TTLS.

The commit 3cae06120a4dd9bebd5f2e57e181ea95e87c8ac4 fixed the issue of
loading the username/password when editing a connection with EAP-PEAP or
EAP-TTLS (using EAPMethodSimple) or EAP-LEAP (using EAPMethodLEAP).

There was a small issue when you edited such a connection: when opening
the configuration dialog, the 'Apply' button was disabled until you switched
to the security tab.

The problem was, that in order to enable the 'Apply' button, 'validate' of
the security dialog will be called. 'validate' looks at the content of the UI
fields whether username and password are set. Due to a bug, they were
unset until 'widget_realize' was called, i.e. not before you switched to the
security tab the first time.

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=1000564

Signed-off-by: Thomas Haller <thaller@redhat.com>
security: don't save CA cert ignore if editing is canceled

Previously the code would update GSettings whenever a security
input field changed and the provided security information had
to be re-validated. This meant the value would be saved even
if the user canceled editing of the connection.  Fix this.

Unfortunately, since only the upper-level code knows when the
editing has been canceled, the upper-level code has to handle
reading the initial values, and saving the new ones.  But that's
easy to do.

Signed-off-by: Thomas Haller <thaller@redhat.com>