Create a command for updating the messages file

[ljacqu]

As we add more messages to the yml file it becomes difficult for server owners to update their YML files without losing their custom messages. Create a child command of /authme that gets new messages from the JAR's messages and adds it to the user's file.

• should we do a backup before changing it?
• if we have a file of the same language (e.g. messages_de.yml), copy missing messages from there
• copy remaining messages from messages_en.yml
  • optionally add them as comments only as our tool task does, but then you need to make sure that the command can be run multiple times without adding the same comment each time
• edit the error message in the Messages class to refer to the new command (the "Error getting message with key...")
• update the commands page (tool task createCommandPage)

Hint: load messages with Bukkit's YamlConfiguration

[ljacqu]

Another idea is to do such a check on startup and adding new messages that are missing, but I'm not sure if it's a good idea to do it without a user's "consent".