Thread safe player interface abstraction

[day-bringer]

Whenever a packet listener is listening for packets asynchronously, it currently returns the player interface, which by default is not thread safe. It would be helpful for developers if it instead returned an instance that was thread-safe. Even if it means most set methods are wrapped in a Bukkit runnable, I feel like there is a way to make more read operations thread safe (such as player.getLocation). Let me know if I'm missing something; the concept of threading/async is new to me.