Add support for backgroundColor and/or backgroundColor.fill

[karpolan]

For Material design backgroundColor or backgroundColor.fill are not supported :(

[joseph-allen]

still doesn't seem to be supported

[lumoe]

This actually works. Although not in full extend, it only supports string, not objects. See: https://github.com/rakannimer/react-google-charts/blob/288ce66a2d8e89012305ee3bb5c200fed0a1c9ef/src/types.ts#L58

Set the backgroundColor property in options.

Example:

<Chart  
    width={"600px"}  
    height={"400px"}  
    chartType="LineChart"  
    data={[  
          .......  
    ]}  
    options={{  
      backgroundColor: "transparent",  
    }}  
  />