Add test

[xavierfav]

Currently we need to manually test the application every time we modify the code which is not very convenient. It would be nice to have some end-to-end tests. We could use a library like protractor-react-selector for that.

A basic first test could consist in:

• four clients connect to the app
• one client creates a room
• the others join the room
• they all choose a name and a set of words
• the game master starts the game
• players go through all the rounds until the end of the game