Converts project into a Lerna monorepo

[ctrlplusb]

Mostly there 👍

What I have done:

• [x] Configured the project as a lerna monorepo, utilising a versioning system that keeps all packages on the same version number. We may want to consider moving to independent versioning.
• [x] Configured yarn workspaces. Yarn workspaces is a must IMO when working with a monorepo.
• [x] Created three packages:
  • react-automata: The core package
  • react-automata-test-utilities: Contains the test helper
  • react-automata-utilities: "Internal" utilities shared between the other packages. May want to consider a rename of this.
• [x] All build/dev tools remain in root of mono repo. You build all 3 packages via the root. I kept the package.json scripts in the root and as they were in order to reduce friction with moving into the monorepo.
• [x] Updated to latest version of babel to get around some issues I was having with running tests at root
• [x] Updated eslint configurations

To be done:

• [ ] Revise the root README
• [ ] Create a README for each package?
• [x] Fix the travis config
• [ ] Validate publishing / versioning works as expected

Build is working, and so are the tests. 👍

Note: when performing updates across the packages you may need to perform a build prior to test. It would be cool if there was a mechanism to build on the fly whilst running tests in watch mode.

Closes #32

[MicheleBertoli]

This is FANTASTIC, thank you very much @ctrlplusb 💖 I'll review and merge ASAP.