implementing PlayerManager, Player interface and PlayerHandler has been modified
accordingly

modified:   include/Player.hpp
modified:   include/PlayerHandler.hpp
modified:   include/PlayerManager.hpp
modified:   include/PlayerStats.hpp
modified:   include/Resources.hpp
modified:   src/player/PlayerHandler.cpp
modified:   src/player/PlayerManager.cpp
modified:   src/player/PlayerStats.cpp
modified:   src/resources/Resources.cpp