Update group name in list when it's changed

[j0hannes]

• I have tested the latest git version

JabRef version 4.1-dev

Steps to reproduce:

1. change group name via "edit group"
2. it's updated under General > Groups but not in the group tree

[Siedlerchr]

You have to collapse/expand the specific group (double click) to make the changes visible. It's a known problem. There is a similar issue about this, which I can't find atm

[j0hannes]

I can't, it's a top-level group without any subgroups. Searching for 'group' and 'name' gave no results.

[tobiasdiez]

Duplicate of #3189.