Add a birthday archives

Also:

* Rename "gift idea" to "gift" everywhere
* Add the date to the next birthdays and past birthdays
`setObject()` doesn't serialize the birthday properties, so it should store the whole `person` objects.
But `allBeforeDate()` should deserialize, replacing `personId` with `person`, so this test should not pass... Or maybe it works because it can't deserialize it, and does nothing, and this ends up with the person object anyway? Or I may just be totally wrong too...