SlimeWorldLoader-s cleanup

[davight]

Additions:

• This adds ability to configure file slimeworld loaders directly inside a config.yml
• This also cleanups a mess around referencing a file loader instead of a abstract one

Changes:

• Removed a need for file loader command. (as they are loaded on startup)
• Added a option to specify loader for clone arg in slimeworld command
• probably some more idk...

TODO:

• Maybe reload loaders when reloading the plugin