Passing width and height to swatches in SketchPresetColors
As far as I'm aware, `<SketchPresetColors />` only accepts the props `Colors`, `onClick`, and `onSwatchHover`. Trying to add styling to that element modifies the container holding the swatches rather than the swatches themselves. The only way to modify the size of the swatches is to go into [SketchPresetColors.js](https://github.com/casesandberg/react-color/blob/master/src/components/sketch/SketchPresetColors.js) and directly modify the `swatchWrap` CSS style, which I'm trying to avoid at all costs. I'd really appreciate the ability to just have width and height (for the swatches) as props of SketchPresetColors. 

For reference, I'm going off the advice from https://github.com/casesandberg/react-color/issues/343