Fixed session handling

SimpleSamlAuth will now always trump MediaWiki when it comes to
creating sessions.
SimpleSamlAuth will call wfSetupSession() in order to allow for edit
tokens.
Because of a bug in MediaWiki where MediaWiki would trump
UserLoadFromSession, we use MediaWikiPerformAction to trump MediaWiki.
Take full control of e-mail for SAML accounts

MediaWiki accounts require an e-mail address, and SAML will override it
every request. Because of this, there is no use in letting users change
their own e-mail settings; they would just disappear.