func drawDisk(color: UIColor, rectForDisk: CGRect = CGRectMake(0.0, 0.0, 1.0, 1.0), withStroke: Bool) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(rectForDisk.size, false, 0.0)
    let context = UIGraphicsGetCurrentContext()

    CGContextSetFillColorWithColor(context, color.CGColor)
    CGContextFillEllipseInRect(context, rectForDisk)

    let rectForCircle = CGRectMake(0.5, 0.5, rectForDisk.size.width - 1, rectForDisk.size.height - 1)
    CGContextSetLineWidth(context, withStroke ? 1.0 : 0)
    CGContextSetStrokeColorWithColor(context,
        UIColor.blackColor().CGColor)
    CGContextAddEllipseInRect(context, rectForCircle)
    CGContextStrokePath(context)

    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image
}