Update Client side data handling

[OliverBenz]

Position class is the representation of the game state.
The SessionManager receives signals from the server and updates the position
The Position class is pure data layer.

The UI elements have a const& to Position.
Position only has public getters. setters are private with SessionManager as friend.

Structure:

SessionManager updates Position
Position emits signals to listeners
Listeners query position for new data.

Then, remove the data getters from SessionManager. UI elements get directly from position class.