Add Val.town plugin configuration and initialization

[Toowiredd]

• nofwl.yml: Add valtown entry under plugins section with name, version, author, description, link, and url fields.
• locales/en.yml: Add entries for plugin categories, tags, dependencies, compatibility checks, and warnings in the settings panel.
• src/main.rs: Add code to load and parse nofwl.yml file, initialize plugins based on configuration, and manage Val.town API endpoints.
• plugins/valtown/meta.yml: Add metadata for Val.town plugin.
• plugins/valtown/main.js: Add JavaScript code to connect to Val.town API endpoints and handle plugin-specific functionality.
• Cargo.toml: Add serde and serde_yaml dependencies.