Even more messages.
Prepare for development on 1.21.4
Shift initial initialization to AsyncPlayerPreLoginEvent. May improve performance on login
Use isDefault function to list default groups
Merge pull request #1418 from stuntguy3000/patch06

Even more messages.
Improve locking on file backend
Add new MultiBackend for multiple-backend handling

Data is split between backends at the entity level.
Add proper toString for PermissionBackend
Another attempt at fixing autoreconnect issues
Fix visibility of timed permissions in /pex user|group <name> commands
Switch back to using Gravity's repo for Updater
Reduce cases where player name is written to user datase, implement more methods for permission subscriptions
Fix up double printing of permissions and informplayers config
Be more forceful with PermissionAttachments
Slight optimization and formatting correction for PermissionList
Force a warning for servers not supporting UUID methods
Move executor code into PermissionBackend, optimize performance of FileBackend a bit
Add more lines to warning message to draw attention
Fix promotion commands to not show UUIDs
Remove usage of AutoCloseable to maintain JDK1.6 compatibility