Add related issue button and epic add issue button

When an issue has no related issues, there's a big and fat panel header that takes up a lot of space and looks intrusive.
It looks especially bad for issues with a small description.

Replace with a simple button.
When you click on a button, you get the full UI to add an issue like usual. If you cancel out, you get back the same simple button.
This button only appears when there are no related issues. Otherwise, you get the same existing UI.
Similar design would be applied to epics too.