Support opening branches popup from all tabs

[kpbaks]

This Pull Request makes it so pressing b opens the Branches popup in all 5 tabs, not only Status and Log tab. This keeps the behavior consistent, and makes the program simpler to use, since you do not have to associate being in a subset of the available tabs, in order to open a, what I would consider, global popup.

The b is not being used in any of the 3 missing tabs, so the change does not conflict with any existing keybinds.

If accepted, I think it would benefit the codebase to have a concept of global keybinds, that are accessible from all tabs, to deduplicate the repeated code to e.g. add a branches keybind.

I followed the checklist:

• [ ] I added unittests
• [x] I ran make check without errors
• [x] I tested the overall application
• [x] I added an appropriate item to the changelog

[extrawurst]

@kpbaks great idea! Why is it draft?

[kpbaks]

Miss-click I think 😅