FR: todo button need to have filter option

[saya6k]

For todos, having customizable filter can make user focus on what he or she has to do.

It can have options like:

items with a due date: boolean upcoming items: int (e.g., if it's 3, count items with a due date within 3 days) to-dos that have no due date: boolean

And this feature should be match with #233