Hacky "threshold" support for user profiles as a cheap anti-spam measure

Site admins (with server access, that is) can set $wgUserProfileThresholds
= array( 'edits' => 5 );, for example, to require users to have five edits
(in qualifying namespaces, see $wgNamespacesForEditPoints) before they're
allowed to edit their own user profile via Special:UpdateProfile.

The actual threshold code is a slightly updated version of the older
threshold code present in other related social tools, such as PictureGame,
PollNY, QuizGame, etc.

Change-Id: I98ecc072b04ba28d3cf29dfc0ef75a8a4ee918f0