This is terrible. It was a mistake to do this before cleaning up the
actual code. It might be better not to use this commit and to do this
refactor in a different order or something.
* Extracted all commands into CustomCommands.cpp
* Moved all chat-related packet handlers into ChatManger.cpp
* Cleaned up redundant includes
* Unified handler naming scheme
* Made all command handlers in CustomCommands.cpp static
