:recycle: lobby code

[fabienjuif]

@WesleyRUCHAUD

I just:

• move some code around
• currified a "context" object to access data that will be in database after that
• use mutation on the lobby list (lobbies)

The purpose of this changes are make the unit testing simpler.

WDYT? Should I merge this is the api-lobby branch?

next: unit testing