Allow variable amount of blur

[Sorgrum]

Provide a prop, blurAmount, which allows the user to control how blurred the placeholder image is.

Usage: Add the blurAmount prop with the amount of desired blur.

<Img
    src={img}
    placeholderSrc={imgSmall}
    bgColor={"#f0f0f0"}
    blurAmount={"5px"}
/>