Bukkit Core Cleanup

This PR does several things:
* Organised imports throughout code
* Changed calls to `getPlayer` to `getPlayerExact` regarding `CPlayer.getName()`
* Shortened primitive check to `class.isPrimitive()`
* Cleaned up code formatting
* Changed `Bukkit.getServer().getPlayer()` to `Bukkit.getPlayerExact()`
* Changed `downloadFile()` in `DependencyManagement` class to use Google Commons IO for downloading (Google Commons IO is included in CraftBukkit)