Add globals and custom transformer to get unit testing working

[matt-hooper]

I managed to get it to the point where the unit tests now run.
To try it, navigate to the perspective-viewer-d3fc folder

• cd packages/perspective-viewer-d3fc
• yarn or npm install
• npm run test:unit

To get the babel to work I had to create a custom transformer (test/transform.js). This also required a workaround found here jestjs/jest#7868

For the d3fc depends on Custom Elements (v1). To avoid getting an error some global variables were required. This will need to be refactored.