Add buffer to Blur

[theruther4d]

When creating the desktop reference, we need to add 2 * the specified blur amount to the total size of the canvas. This way, when blurring things close to the edge of the screen, we won't get empty canvas.

[theruther4d]

This appears to be a bug with Chrome. Even when the <canvas> is bit enough and fully painted, being too close to the edge causes the fade-out on the right.

In the image above, the canvas overlaps the screen to the right by another 20px, but it doesn't appear that way.