Fix for issue 6959

[luis-valdez]

Fixes #6959 implementing the method needsSharedDatabase in the ActionHelper and then binding it in the class PullChangesFromSharedDatabase. This solution prevents the user from clicking "Pull changes from database" if a shared database is not present.

When the DatabaseLocation is local:

When the DatabaseLocation is shared:

When there is no library open:

• Change in CHANGELOG.md described (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]

Please have a look at the failing checkstyle check.
Can you also please test the case when no library is open? e.g. all tabs closed?

[tobiasdiez]

Thanks! Two minor remarks from my side, then this is good to go!

[tobiasdiez]

Thanks!

[luis-valdez]

Thanks for letting me contribute, I'll pick up another issue

[Siedlerchr]

If you could fix the remaining checkstyle errors it would be fine:

 Error: eckstyle] [ERROR] /home/runner/work/jabref/jabref/src/main/java/org/jabref/gui/actions/ActionHelper.java:9:1: Wrong order for 'javafx.beans.binding.Binding' import. [ImportOrder]

Error: eckstyle] [ERROR] /home/runner/work/jabref/jabref/src/main/java/org/jabref/gui/actions/ActionHelper.java:22:1: 'com.tobiasdiez.easybind.EasyBind' should be separated from previous imports. [ImportOrder]
> Task :checkstyleMain

[Siedlerchr]

Thanks again for your contribution!