Course storage change:
- courses are now stored in json instead of yaml.
- this means that any of your current courses need to be converted to json or they won't be loaded into the plugin (this can easily be done with a converter, https://onlineyamltools.com/convert-yaml-to-json for example)
- this was done because spigot 1.21.3 started using a version of a dependency I was using for yaml deserialization and they were conflicting causing errors I didn't know how to resolve.

Made a few changes so that the plugin is now compatible with Spigot, whereas previously, it was only compatible with Paper.