Game state is now initialized for real.

Here is the checklist to make everything work before Monday. 
Some of this points should have been avoided with more experience, how can we be sure that we will be driven by something to avoid them?

- [x] board is nil in the game loop data
- [x] gen_fsm:reply/2 wants the first parameter to be the From provided to the callback function (so that {pid(), reference()}) but we are using it with only a pid() in the game (rows 65 and 66)
- [x] tick messages is a string in the macro at line 10, atom is better because it is used in the callbacks
- [x] tick messages arrives out of band in the `handle_info/3` so that at the moment we remain stuck forever in state `play`
- [x] player:join/2 should send a message to the gen_server because now we are in process and the message is not sent by the player process but by the calling process

Points 3 and 4 are due to the presence of the ticker. I wuold like to have an acceptance and only after remove it.