[Feature Request] Add filtering for tasks

[RedSparr0w]

Add a button/filter to show only incomplete/completed tasks in the current list

[tztokjeffy]

If no one is working on this I can give it a go. Took me only a few minutes to remove the completed tasks from the UI, but need a bit more work to collapse the remaining tasks after they were filtered

[rmobis]

If no one is working on this I can give it a go. Took me only a few minutes to remove the completed tasks from the UI, but need a bit more work to collapse the remaining tasks after they were filtered

PRs are welcome =). Just let me know how you're planning the UI for that.