Accept user IDs as well as names for manual achievement (un)?locking, as well as a warning fix for optout.

 * #theme => 'achievement' usage has gained contextual theme suggestions.

Tweaked PDO query to return associative arrays to stop a few forced typecasts, and fixed all usages of achievements_totals_users().

Load and cache all of a user's unlocks in achievements_unlocked_already() for a performance boost on heavier sites.

JS popups can now handle multiple achievements, and unlocked achievements can now be configured to remain in defined order (versus being sorted to the top).