Introduce PixelRegion.overlaps

[adonath]

For some use cases e.g. when placing regions algorithmically a method like PixelRegion.overlaps(other_region) would be useful. This will be easily to implement once e.g. CompoundRegion.area is supported (see #433). In this case the implementation would reduce to:

def overlaps(self, other):
    intersection = self.intersection(other)
    return intersection.area > 0

For some specific cases it could also be implemented analytically if needed.