Install dependencies for the basic testing setup

- (dev) @babel/core
- (dev) babel-jest
- (dev) babel-plugin-react-remove-properties
- (dev) babel-preset-gatsby
- (dev) identity-obj-proxy
- (dev) jest
- (dev) jest-dom
- (dev) react-testing-library

References:
  (1) https://www.npmjs.com/package/@babel/core
  (2) https://www.npmjs.com/package/babel-jest
  (3) https://www.npmjs.com/package/babel-plugin-react-remove-properties
  (4) https://www.npmjs.com/package/babel-preset-gatsby
  (5) https://www.npmjs.com/package/identity-obj-proxy
  (6) https://www.npmjs.com/package/jest
  (7) https://www.npmjs.com/package/jest-dom
  (8) https://www.npmjs.com/package/react-testing-library

GH-39