Make all lessons importable on codesandbox

[NicolasRannou]

• Create src subdir.
• Create package.json.
• Organize files as in lesson 00.

• [X] Lesson 00: https://github.com/FNNDSC/ami/tree/dev/lessons/00
• [ ] Lesson 01: https://github.com/FNNDSC/ami/tree/dev/lessons/01
• [ ] Lesson 02: https://github.com/FNNDSC/ami/tree/dev/lessons/02
• [ ] Lesson 03: https://github.com/FNNDSC/ami/tree/dev/lessons/03
• [ ] Lesson 04: https://github.com/FNNDSC/ami/tree/dev/lessons/04
• [ ] Lesson 05: https://github.com/FNNDSC/ami/tree/dev/lessons/05
• [ ] Lesson 06: https://github.com/FNNDSC/ami/tree/dev/lessons/06
• [ ] Lesson 07: https://github.com/FNNDSC/ami/tree/dev/lessons/07