Allow OAuth login on the (upcoming) new forum

[xan2622]

Some people (players) who already have a GitHub account might find very interesting the idea to be able to log in the forum with their Github account. Simple, no need to create another account.

PHPBB 3.1 already features OAuth2 login but I have found some interesting plugins, links:

• https://github.com/Lusitanian/PHPoAuthLib
• https://github.com/oneall/social-login-phpbb