Refactor SaveOrderConfigPanel

[calixtus]

A messy job, that was on my ToDo list for some time now.
I gave the SaveOrderConfigPanel an overhaul to make it a little bit more generic and to be able to work with more than three SortCriteria.

Before:

After:

One Problem remaining is that the preferences do only allow three SortCriteria for Export at all with the current JabRefPreferences implementation. Changing that would mean I would have to add PreferenceMigrations OR i just allow three SortCriteria for now in the Export prefs tab.

Yet some very little issues left, i hope i can fix them the next days.

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[Siedlerchr]

Good! While you are at it, can you please take a look at https://discourse.jabref.org/t/sort-order-for-export/2598/12

[calixtus]

Hmm... I think I unintentionally stumbled over a bug in the tests.
The 'expected' value of in the test bib file is

while the test states that

EDIT: No, understood it wrong.

[calixtus]

Good! While you are at it, can you please take a look at https://discourse.jabref.org/t/sort-order-for-export/2598/12

I noticed, that when i change the number of criterias and save it, JabRef complains about the file being saved by another program. Could have something to do with it?

I can take a deeper look into this, but I'm somewhat careful, because I don't want this PR to explode beyond dealing with the visual representation. Let's see where this is going.

[calixtus]

DevCall decision:

• limit in preferences export to 3 criteria
• debug https://discourse.jabref.org/t/sort-order-for-export/2598/12 in a followup pr

[koppor]

Fixes JabRef#510