Add react-dom to the devDependency list for React Native projects

[matt-oakes]

Issue: Closes #1099

What I did

I have added a check to see if react-dom isn't already in either the dependencies or devDependencies of the React Native project when getstorybook is run. If it isn't, it will add it to the devDependencies of the package.json.

How to test

Testing adding

1. Create a React Native project without react-dom as a dependency.
2. Run getstorybook.
3. yarn run storybook should run without further steps.

Testing ignoring

1. Create a React Native project with react-dom as a dependency.
2. Run getstorybook.
3. yarn run storybook should run without further steps and the react-dom dependency should not have been touched.