Gradient graphics context

[traviskirton]

Updates gradientFill to render a graphic and create a C4Color from a UIColor from a tiled image.

Fixes: #608

[traviskirton]

NOTE: When animating between a color and a pattern there is a flicker to white. This seems to be a bug in UIKit as it occurs for a UIView as well.

    var isColor = true
    override func setup() {
        let r = UIColor.redColor()
        let p = UIColor(patternImage: UIImage(named: "pattern2")!)

        let v = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        v.backgroundColor = r
        canvas.add(v)

        canvas.addTapGestureRecognizer { (location, state) -> () in
            C4ViewAnimation(duration: 1.0) {
                if self.isColor {
                    v.backgroundColor = p
                } else {
                    v.backgroundColor = r
                }
            }.animate()
            self.isColor = !self.isColor
        }
    }

[traviskirton]

Closing, moving changes to 1.1.x