grid: fix sticky=>'n' and sticky=>'s' positioning

[HaraldJoerg]

The sticky option for gridConfigure works opposite to what I expect for sticky => 'n' and sticky => 's'.
My example code (again derived from your grid example with small changes):

use 5.020;
use strict;
use warnings;
use Prima qw(Application Label);

my $w = Prima::MainWindow->new(
    backColor => cl::Gray,
);
$w->insert(
	[Label => name => 'north', backColor => cl::Red],
	[Widget => name => 'g', backColor => cl::Green],
	[Label => name => 'south', backColor => cl::Blue],
	[Widget => name => 'y', backColor => cl::Yellow],
);

$w->gridConfigure(north => row => 0, column => 0, sticky => 'n');
$w->gridConfigure(g => row => 0, column => 1,);
$w->gridConfigure(south => row => 1, column => 0, sticky => 's');
$w->gridConfigure(y => row => 1, column => 1);

run Prima;

This puts the "north" label at the bottom of its cell, and the "south" label at its top:

The patch swaps the north and south alignments, now it looks how I would expect it: