Internal redesign

- Add final keyword where possible
- Add CommandMethod representing a command method with several commands
or sub commands
- Registered commands now use the command method
- Add some options if the permissions should be inherited for
subcommands
- Remove unneeded permission handler
- Fix some only players problems with subcommands
- Only players will now recognised when using Player as first variable
instead of CommandSender
- Some more things; I can't remember :D