Fix #5398

Ordering the home timeline query by account_id meant that the first
100 items belonged to a single account. There was also no reason to
reverse-iterate over the statuses. Assuming the user accesses the
feed halfway-through, it's better to have recent statuses already
available at the top. Therefore working from newer->older is ideal.

If the algorithm ends up filtering all items out during last-mile
filtering, repeat again a page further. The algorithm terminates
when either at least one item has been added, or if the database
query returns nothing (end of data reached)