Add mapThemrProps option

[javivelasco]

This PR brings a new option and property to the decorator than can be very useful in some scenarios. Until now, we were passing a ref prop always to the decorated component with the withRef property. This is not always the case: picture that you have a component that is decorated already with an HOC that maps innerRef to ref. For those cases you can use the new mapThemrProps option/prop.

It receives all properties given to the component (included themr ones) and the generated theme object and it should return the properties that you want to pass down. For the exposed scenario you might want:

function mapThemrProps(props, theme) {
  const { composeTheme, innerRef, mapThemrProps, themeNamespace, ...rest } = props;
  return { ...rest, withRef: innerRef, theme };
}

Check the tests to see a full use case.

[javivelasco]

This needs an update of typings @raveclassic

[javivelasco]

Backwards compatible so merging :)