New Features:
- Added AdvancementManager#unloadProgress(UUID uuid), AdvancementManager#unloadProgress(UUID uuid, String namespace) and AdvancementManager#unloadProgress(UUID uuid, Advancement... advancements) (only works for online Players)

Bug(s) fixed:
- Granting an advancement that isn't visible will now show a toast if it is set to (if other advancements get revealed in the process which are granted, they will also show a toast, but if you don't change it, they are always visible when they are granted so shouldn't be a big deal)