[WIP] Introduce Redux

[willdurand]

This is not going to be fun, but this is definitely needed...

Purpose

In this PR, I refactor the whole project to introduce Redux and get rid of
our very own Store. This was nice to learn and play with React, but now we
are reaching the limits of this part. Hence this refactoring to use Redux
instead, as we did for Franklin for instance.

Features

• Install Redux et al.
• Refactor components into logical units
• Make the component tests pass again
• Rewrite the Store into a Redux store (using modules and redux-ducks)
• Port all existing tests
• Maybe write a few more tests
• Maybe rename a few methods as our conventions slightly evolved since
  the beginning of this project (e.g., onSomething() vs
  handleSomething())

Also...

• Fixes Aggregate identical messages so they only appear once #107
• Fixes MessageBox removal is broken #143
• Merged Add a share modal #171

New Features

• Shortcut: Cmd+B for surrounding a selection with ** (bold/strong)
• Shortcut: Cmd+I for surrounding a selection with _ (italic)
• Shortcut: Cmd+Z for undo

It is also possible to change the template of the default document without creating a new "working" document. A "working" document gets created when the content is changed.

ETA

No ETA yet. Hence, contributions should be delayed as most of the code will
be affected.

[willdurand]

I am more and more convinced that having a separate routine for the synchronization is not our/my best idea..

[willdurand]

Ok, that looks good to me now. Let's test it.

[willdurand]

To fix:

Warning: Failed prop type: Required prop `forceUpdate` was not specified in `Editor`.
    in Editor
Warning: Failed prop type: Required prop `forceUpdate` was not specified in `Markdown`.
    in Markdown

[willdurand]

Deployed last version (c1a2eeb) into production for 12-24h (with Sentry).

If you want to give it a try, browse https://monod.lelab.tailordev.fr/. If you don't have the latest version (see bottom right), close all your Monod tabs, then reopen https://monod.lelab.tailordev.fr/ again (that's how service workers work...).

Next:

• if you cannot load your existing documents, please let me know
• if you get new forks of your current document for no reasons (e.g., you are working alone), please let me know
• if you get a weird experience, I am interested too
• otherwise, Sentry should collect all other errors

[willdurand]

🎆 🔥 ⭐ 🌟 🌠