Change tab selection order

[DvP17]

Problem

Hard to navigate groups via keyboard because long tab selection sequence and no key binding to focus on groups.

Solution

Change tab selection order in a common way (e.g., windows explorer or mozilla thunderbird)

Tasks

Preview Give feedback

1. When entry table is focused press shift + tab to focus on groups
2. When groups are focused press tab to focus on entry table

Context

https://discourse.jabref.org/t/key-binding-to-focus-groups-interface/3803

[koppor]

This is a sub issue of #1225.

[koppor]

Note that we even have a blog entry on a revised hotkey system at https://blog.jabref.org/2016/08/15/HotkeyRevision/.

I think, the workaround with Alt+3 does not solve the issue here.