Fix EllipseShape for Affectors in QtQuick.Particle

EllipseShape was theated like rectangles if set as shape in an Affector
due to an unimplemented containment check (was marked as TODO in source
code). This fix implements the missing check.

Change-Id: I8df1406f147c56e799531fccf4963110c9fdd8ef
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>