core: fix GtkBuilder-related performance issues
GtkBuilder isn't as quick as libglade when building the widget tree from the XML file, so the previous handling of wireless security and EAP methods caused connection editor display times of 4 seconds or more on slower machines (like 1.7GHz Pentium M). Previously, all security and EAP UI was stored in one glade/builder file which was re-read from multiple places. With glade that was fine, but GtkBuilder's gtk_builder_add_from_file() takes quite a bit longer than glade did. So split each piece security and EAP UI description out into a separate file, and consolidated handling of UI building into the EAPMethod and WirelessSecurity classes instead of doing it in the subclasses.
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