Properly and persistently stores which players have beaten which arenas
Adds a hopefully fully functional DropperArenaGroup class
Stores arena groups in the arena handler
Adds a lookup map to improve performance of getting arena by name
Adds saving and loading of groups
Adds all necessary checks for whether players have beaten the required dropper arenas before joining
Removes stage from arenas
Adds a test to make sure changing the order of arenas in a group works as intended
Makes the type of block players have to hit to win configurable
Separates the velocity option into vertical and horizontal velocities
Reduces some redundancy when getting an arena from an arena name
Partially implements the list command
Tries to improve the handling of players exiting in the middle of a session
Adds missing comments to ArenaStorageKey
Removes some finished TODOs
Registers all listeners
Registers all commands
Adds more descriptive TODO comments to each command
Removes unintended double storage of dropper arena sessions in DropperArenaHandler
Adds commands and permissions to plugin.yml
Uses the Spigot API instead of the Paper API
Reduces the Java version to 16, just in case.
Adds a lot of empty classes to show the intended plugin structure.
