make filter operator select focusable and keep track in query filters di...

https://www.openproject.org/work_packages/15301

I have made a small change in that now when you add a filter it always gets added as the last filter. Previously if you deleted a filter and then added it again it would have appeared where it was the first time. I changed this purely to make it easier to focus on the last element when you add it but also I think it makes more sense this way.