Add DiscordSRV Hook

[Dinty1]

This adds a hook into DiscordSRV which will allow VanishNoPacket to:

• Broadcast fake join messages to Discord.
• Broadcast fake quit messages to Discord.

It will also add the following things to facilitate this:

• hooks.discordsrv config option (config version has been bumped to 8 and old configs will be updated).
• vanish.hooks.discordsrv.broadcastfakejoin and vanish.hooks.discordsrv.broadcastfakequit permissions.
• Hook methods that trigger whenever someone fake joins/quits (onFakeJoin and onFakeQuit).

I have tried to extensively test and follow the current format, but if something isn't quite right I can be contacted either here or on Discord (Dinty#4988).

It should also be noted that the latest stable build of DiscordSRV does not cancel leave messages of players who are vanished with VanishNoPacket, however this has been fixed in the development build.

[mbax]

Thanks! Not sure I'll get the chance to look at this until the weekend, but I wanted to pop in now to say it :D

[mbax]

Pulled, thanks!

https://github.com/mbax/VanishNoPacket/commit/290427df62a8f2e01d7f9aeb30da12618616df2b