Analytics: Add "hide empty date buckets" option

[Bone008]

Use case: I want to investigate average monthly expenses in 2019, but excluding the month February because it was exceptional for some reason.

So I filter by date:2019 -date:2019-02 and want to see averages for the remaining 11 months, not 12. Should be an explicit toggle to avoid confusion when buckets simply have had no transactions.