Send and receive player positions on the client side

[gioragutt]

As a first step of establishing the client-server comm protocols,
A good first step is to first see all players in the map.

There's a basic ColyseusClient script that is copied from the tutorial which does something basic, and can be a good place to start. It should be cleaned from crap, wherever possible.

This requires coordination with the person implementing the server side - so watch out for that.