data_manager:
added get_all()
data_manager:
added get_all_containing_as_map_as<T>(...)
added data_store class:
taking a ref or a pointer to the different types
avoid copying (as with sf::data_manager::get_as<T>(...))
game_handler:
added data_store (currently just with sf::Texture as storage)
itembar:
avoid copying the textures by using new data_store