Fix moving an item up

[dmarkow]

Because the query to find the two previous items wasn’t sorted in descending order, it would always return the first two items in the list (positions 1 and 2), not the two items immediately before the item we want to move up. For nearby_query on an item in the 10th position would return the 1st/2nd items, not the 8th/9th.

The existing test didn't catch this because it was only using a 3-item list. I updated the test with 4 items, moving the 4th item up to make sure it goes between the 2nd/3rd items (instead of the 1st/2nd). Solution was to update the nearby_query function to accept an order_by direction.

[dmarkow]

This exclude call is needed because rank_query already sets the order to be ascending on the rank field, so setting a descending order on the next line would be ignored.