Feature request: Aggregate todos across files

[blakedietz]

Had a discussion with @CaptChrisD and he mentioned that it would be helpful to have a way to aggregate tasks across tags.

So for file 1

<!-- @nested-tags:house/todo -->
- [ ] Cleanup wiring in garage
- [ ] Cleanup wiring under garage

And file 2

<!-- @nested-tags:house/todo -->
- [ ] Tear out chimney

You would have a way to aggregate tasks into a single list in the ui.