Add "WePlay" support

[csssuf]

Some Last.FM IRC bots support a feature called "WePlay", where a /wp command shows what each channel member is playing at the moment. Typically the feature is opt-in, and users can opt-in with a single command.

This would involve adding a new database table for tracking WePlay status per-channel. It would likely need to keep track of tuples of (team_id, channel_id, and user_id). Once that's added, invoking the command would simply require checking the list of enabled users for the given channel and invoking the normal np logic serially.