revamp how $add selects media about yukari

[d-dd]

Using the queue table may be a good idea.
Select mediaId's from the Queue table that has been queued in the past week (for example, or could also be a number such as playlist length + 100). Call this Recent
Take a random sample from the complement of Recent and Queue. Result would be non-recent media. Therefore there is no worry of queuing a video already in the playlist (unless the playlist is older than one week). This wouldn't really work for narrow searches, because it may return nothing too often. This doesn't solve the problem of the queued media being invalid.

[d-dd]

SELECT mediaId from Media where mediaId NOT IN (SELECT mediaId FROM Queue ORDER BY queueId DESC LIMIT 100) ORDER BY RANDOM() LIMIT 6;

[d-dd]

8963f3e is decent enough.