Chat module: literally just renaming some stuff

[RedFlames]

This isn't strictly necessary, but it is what I based my rewrite of the command arg parsing on, so I'm PR-ing this first in the hopes that the other PR will have nicer diffs (the other PR was made on top of this one)

What I did here:

• give all the chat command classes and stuff the namespace Celeste.Mod.CelesteNet.Server.Chat.Cmd within the chat module
• Rename everything that had the ChatCMD prefix, I mostly just replaced that with Cmd although I think in some places I did something else. This is really just an "aesthetics" refactor >w>
• some examples:
  • ChatCMD -> ChatCmd (could maybe rename this to Cmd as well, but idk)
  • ChatCMDChannelChat -> CmdChannelChat
  • ChatCMDTP -> CmdTP
  • ...
  • ChatCMDArg -> CmdArg
  • ChatCMDArgType -> CmdArgType
  • ChatCMDEnv -> CmdEnv
• Oh and I did set the readonly ChatModule Chat field in CmdEnv to private because only CmdArg was only using it to get to CmdEnv.Chat.Server which now goes through CmdEnv.Server instead. CmdBan was doing a similar thing.

I didn't actually delete/add any files, that's just git not picking up on my renamed files. 🙂