refactor: Map should not accept a backgroundColor prop

[WickyNilliams]

By accepting backgroundColor as a prop, any change to the hue slider will always cause a re-render of map (as the bg hue changes). if we move this prop to another div (in ColorPicker?), or compose a ColorMap from a Map, we can avoid a re-render of Map:

var ColorMap = React.createClass({

  render: function() {
    return (
      <div style={{ backgroundColor : this.props.backgroundColor }}>
        <Map
          x={this.props.x}
          y={this.props.y}
          max={this.props.max}
          onChange={this.props.onChange}
        />
      </div>
    );
  }

});