Remove entries from prior groups if move operation is selected

[lenhard]

Fixes #3101

There is one problem left to conclude this. It does the proper operation on the selected entries and updates the group tree. However, it does not update the coloring in the group tree. @tobiasdiez Could you give me a hint on how I can achieve this?

• Change in CHANGELOG.md described
• Tests created for changes
• Screenshots added (for bigger UI changes)
• Manually tested changed features in running JabRef
• Check documentation status (Issue created for outdated help page at help.jabref.org?)
• If you changed the localization: Did you run gradle localizationUpdate?

[tobiasdiez]

The code looks good to me.

In order to update the status, you need to tell the group tree that the selected entries changed (not the selection changed but the properties of the entries).
The cleanest solution is to use an extractor here https://github.com/JabRef/jabref/blob/master/src/main/java/org/jabref/gui/StateManager.java#L37, see for example https://stackoverflow.com/questions/31687642/callback-and-extractors-for-javafx-observablelist.
However, an explicit StateManager.setSelectedEntries(StateManager.getSelectedEntries()) should also work.

[lenhard]

Unfortunately, using the StateManager does not solve the coloring for me.

But to be honest, it seems rather broken anyway, irrespective of this PR. I have a database with 3 entries and 2 groups. The only way to get a coloring is to click an entry with a group in a newly started JabRef without opening the entry editor. That coloring never changes even if I click different entries. Does coloring actually work for you?

I think this PR is ready to go. Someone else should check the fix in a running JabRef. The coloring problem should be investigated in another issue/PR.

[tobiasdiez]

In general it works for me but I also noticed that sometimes the color is not updated. Probably related to #2857.