The old way of checking for focus loss caused GTK to be unable to
even open the combobox. This way checks for the event sent when the
list closes and uses that to close the grid editor.
Fixes https://gitlab.com/kicad/code/kicad/issues/4617
ADDED Eeschema-specific netclass settings including wire and bus
thickness, color, and line style.
Netclasses override individual wire & bus colors and line styles.
If that proves an issue we might look at something more sophisticated
with inheritance.
Fixes https://gitlab.com/kicad/code/kicad/issues/4581