added Server instance, userManager and roomManager gets it's reference
in their singleton classes, server objects are now passed to the
BaseEventHandler, newly connected users' id are now thesame as the
connection id (connection objects are now not part of the User),
refactored code in getting rooms, adds the user in the room that is
joined, removes the user in the room that is left
passed the server instance to the listener
added the server instance passed from the listener, refactored code to
get connection objects based on the user's id
refactored event handlers