Config refactor + add option for disabling logging on world loading

[dxnnv]

This PR cleans up the configuration file, and adds the option to disable hologram loading log messages when worlds are loaded. The new config.yml is as follows:

saving:
  autosave:
    enabled: true # Whether autosave is enabled.
    interval: 15 # The interval at which autosave is performed in minutes.
  save_on_changed: true # Whether the plugin should save holograms when they are changed.
logging:
  log_level: INFO # The log level for the plugin (DEBUG, INFO, WARN, ERROR).
  log_on_world_load: true # Whether hologram loading should be logged on world loading. Disable this if you load worlds dynamically to prevent console spam.
  version_notification: true # Whether the plugin should send notifications for new updates.
visibility_distance: 20 # The default visibility distance for holograms.
register_commands: true # Whether the plugin should register its commands.

This simply organizes the configuration for improved readability by nesting common options and ordering them properly. mute_version_notifications has been refactored to logging.version_notifications to make the option more intuitive (true = sends notifications, false = does not send notifications). All files and method names have been updated accordingly.

The option logging.log_on_world_load provides the ability to disable messages such as:
[FancyHolograms] (FancyHolograms-Holograms) INFO: Loading holograms for <worldname>
This allows server operators to prevent FancyHolograms from spamming console on servers that load/unload worlds dynamically (especially worlds that have no holograms, which makes these messages redundant).