ADDED zone_connection constraint.
ADDED thermal_relief_gap and thermal_spoke_width constraints.
ADDED angle override for thermal relief spokes in Pad Properties.
Fixes https://gitlab.com/kicad/code/kicad/issues/4067
ADDED arc, circle and rectangle shapes for schematic. Shapes support
line styles and fill colors.
CHANGED sheet background color in Edit Text & Graphics Properties to
fill color (and it now affects shapes).
Pushed STROKE_PARAMS down into common and moved all shapes to using it
for stroke descriptions.
Jeff Young