Introduce new messages config

[Adammatthiesen]

This pull request introduces a new MessagesConfig configuration class to centralize all user-facing messages and error strings, replacing hardcoded messages throughout the codebase. This change increases maintainability and makes it easier to customize messages without modifying code. The update also refactors command logic to use these configurable messages and cleans up the previous approach of storing error messages in MainConfig.

Centralized Message Configuration

• Added a new MessagesConfig class that holds all success and error messages, and integrated it into the configuration manager (CobbledLevelControlConfigManager). [1] [2] [3] [4] [5]
• Removed the old errorMessages section from MainConfig, consolidating all message strings into the new config. [1] [2]

Command Logic Refactoring

• Updated all command handlers in LevelControlCommand.java to use messages from MessagesConfig instead of hardcoded strings, improving consistency and enabling easier localization or customization. [1] [2] [3] [4] [5] [6]

Consistency and Bug Fixes

• Standardized checks for unset difficulties to use RuntimeDifficulty.emptyDifficulty instead of the string "none", ensuring consistent logic throughout event listeners and commands. [1] [2] [3]

These changes make the codebase easier to maintain and extend, especially for users who want to customize in-game messages.