Rough version.
- Introduces a limbo player state on the LimboPlayer, allowing us to add further mandatory actions between successful (password) authentication and the ability to play on the server
- Overloaded method with (String, String...) as args was problematic as it could be confusing on its own and also confusing with the (CommandSender, String...) flavor
- Remove abstract captcha manager in favor of a primitive captcha code storage (composition over inheritance)
- Supply player when checking captcha code for further usage (fixes open point from previous commit)
- Add methods to LimboService for handling messages to make it the only relevant Limbo class for outside classes
- Move LimboPlayerTaskManager to limbo package and make it package-private
- Create MessageTask and TimeoutTask immediately when LimboPlayer is created
- #1112 MessageTask: improve efficiency by keeping reference to Player
