Add support for Forge 1.7 clients & servers.

Add support for Forge servers running build 1210 and above (currently on the Forge "new" branch). See issue #899 for the issue that has been tracking this. Contains code by @jk-5, @dualspiral & @bloodmc -  thanks to everyone who has been involved in the process.

Adds the following:

* Addition of code to facilitate the Forge handshake between client and server (using the addition at https://github.com/MinecraftForge/FML/pull/504)
* Updates the legacy read/write array methods in the DefinedPacket methods
* Adds an API call to get the mod list of a user, if this is known

This PR contains the ByteBufUtils from Forge by cpw with permission to enable reading and writing of large Forge packets. 

We have seen that some client side mods may crash whilst behind Bungee at the present time - this is due to some mods not expecting a reset packet. Known mods where this is the case have been notified, or are in the process of being notified.

Compatibility with Vanilla has not been affected.

(I will pop into Spigot's IRC if necessary - please let me know if this is needed.)