Update to UUIDs

I updated it to use UUIDs instead of playernames. There is no converter (yet) for old configs.

Added the automatic import of the whitelist (whitelisted players will set as members) on the first start with the plugin (it checks if the users.yml exists).

I also changed the colors of the disconnect messages from white to yellow/red and added a config option (broadcast-failed-logins) to disable the ingame messages if a player joins who was not invited yet to have an ability to disable spam by noninvited players.