Rename some methods, add SinkLogger interface and some minor internal changes

* SinkLibrary: Rename getUser(UUID) to getIngameUser(UUID)
* SinkLibrary: Rename getUser(Player) to getIngameUser(Player)
* SinkLibrary: Remove sendIRCMessage(String)
* SinkLibrary: Add getUserExact()
* SinkLibrary: Add getIngameUserExact()
* Logger: Rename warning(String) to warn(String)
* IngameUser: Remove IngameUser(Player) comstructor, use IngameUser(UUID) instead
* Replace Bukkit.getPlayer() and Bukkit.getOnlinePlayers() with BukkitUtil.getPlayer() and BukkitUtil.getOnlinePlayers()