JabRef should not show completed tasks

[koppor]

We tried to remove finished tasks at #11574. However, JabRef did not shut down then (#11574 (comment)).

We reverted that PR at #11818.

Better solution: Get controlsfx/controlsfx#1567 done and include it.

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Discussion:

Removal of finished background tasks was added, because during summer, each indexed PDF was appearing as background task. That lead to thousands of tasks and lead to UI issues. Now, it seems that both AI (@InAnYan ) and Lucene (@LoayGhreeb) do a summary task. It would be OK to keep the finished tasks.

Currently, finished tasks cannot be removed by a user: controlsfx/controlsfx#1559

My proposal:

Investigate 5 hours either in fixing the exception in JabRef - or add the functionality to remove the finished tasks in TaskProgressView .

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• Refs JabRef doesn't quit InAnYan/jabref#178.
• Refs BackgroundTask interrupted when shutting down JabRef LoayGhreeb/jabref#6