Support Wikimedia OAuth

[Pathoschild]

Let users authenticate/authorize with Wikimedia OAuth (once for all tools). This will enable some interesting features in the future:

• user preferences (like opt-in);
• query history (see the queries you ran recently);
• roles (like checkuser-only tools);
• self-serve Synchbot;
• self-serve StewardBot;
• crosswiki watchlists?

[Pathoschild]

I moved this issue to Pathoschild/Wikimedia-contrib#30 as part of the repository merge.

[bihcode]

Bosna i Hercegovina