Aborting Tasks when something is hung does not abort the hung task.

[maforget]

Describe the bug
If something is hung aborting all task clears the queue, but the hung thread is still processing so anything added after it stays in limbo until we close the program or the task finishes.

Aborting should stop everything (safely).

Exact Steps to Reproduce
I was able to partially reproduce the problem:

• I queued a couple of exports and intentionally added a 1 minute pause inside the exporting to reproduce some kind of locking.
• If I would abort all thread, the thread list would disappear but the icon on the taskbar still indicates that it is still exporting.
• Starting another export during that time would add the export in the dialog in waiting state.
• They would only proceed once the pause I've added was elapsed. Even with all tasks aborted, it still needs to complete it's task before it can be set to a completed state.