Add: MUI theme support for react-select

[wongyiuhang]

This PR is trying to pass Material-UI theme context to react-select, in order to support dark theme.

Closes #14

[seveibar]

thanks @wongyiuhang! reviewing now...

[seveibar]

this should be part of a global context or in a single file, in react when you define objects in component props it causes a lot of rerenders- it COULD be a problem from a performance perspective and it's a problem from a DRY perspective.

[wongyiuhang]

I understand your concern, however, the theme really would change on some rare occasions, for example, switching between light mode and dark mode.

Is that okay, if I somehow "memorise" the colors object, therefore reduces the re-rendering of the object?

[wongyiuhang]

const themeColors = useMemo(() => ({
  primary: MUItheme.palette.primary.main,
  primary75: MUItheme.palette.primary.light,
  primary50: MUItheme.palette.primary.light,
  primary25: MUItheme.palette.primary.light,
  neutral0: MUItheme.palette.background.paper,
  neutral5: MUItheme.palette.grey['50'],
  neutral10: MUItheme.palette.grey['100'],
  neutral20: MUItheme.palette.grey['200'],
  neutral30: MUItheme.palette.grey['300'],
  neutral40: MUItheme.palette.grey['400'],
  neutral50: MUItheme.palette.grey['500'],
  neutral60: MUItheme.palette.grey['600'],
  neutral70: MUItheme.palette.grey['700'],
  neutral80: MUItheme.palette.grey['800'],
  neutral90: MUItheme.palette.grey['900']
}), [MUItheme])

<AsyncSelect
  ...
  theme={theme => ({
    ...theme,
    colors: {
      ...theme.colors,
      ...themeColors
    }
  })}
  ...