Make the Config languages and services keys required

[remcohaszing]

This provides a slightly more convenient interface for server plugins. The default is defined with a null prototype, so it doesn’t have predefined keys.

For example, this allows for the following change in the MDX language server:

- config.languages ||= {}
  config.languages.mdx = getLanguageModule(plugins)
- config.services ||= {}
  config.services.markdown = createMarkdownService()
  config.services.typescript = createTypeScriptService(modules.typescript)

[johnsoncodehk]

Closed because since #113, the language server no longer supports the default config file. thanks!