Added Yggdrasil Authentication System

Code by Howaner.  Fixes/Changes by me.
Code Update
Fixed Error?
Fixed mistake
Initial 1.7.6 protocol support.

Doesn't work yet because of missing UUIDs.
Merge remote-tracking branch 'daniel0916/YggdrasilAuthentication' into Proto176
A client UUID is generated when the server is in offline mode.

1.7.9 client works with these changes in offline mode.
Implemented the 1.7.6 protocol and authenticator.

Server works both in online and offline modes with 1.7.9.
Merge pull request #888 from mc-server/Proto176

Protocol 1.7.6