Backspace and delete don't do anything when the annotation list is in focus

[petebankhead]

Bug report

Describe the bug
When using the annotation list (under the 'Annotations' tab), pressing backspace or delete doesn't do anything.

If feels like it should. To actually delete any objects, a user needs to either press the 'Delete' button below the list, or click on the viewer to activate it. This feels cumbersome, and can result in accidentally changing the selection or drawing something in a viewer, depending upon what tool may be selected at the time.

To Reproduce
Steps to reproduce the behavior:

1. Draw some annotations
2. Click inside the annotations list to activate it (and select something)
3. Press backspace
4. Observe... nothing really

Expected behavior
Backspace or delete should work for the list.

Desktop (please complete the following information):

• QuPath v0.3.0 (and earlier)

Additional context
Issue highlighted by @tp81 at #830