Use ctrl+arrow to switch focus between panes in the status tab

[alexmaco]

Currently, the only way to switch between the tree and stage is by scrolling through the entire list.
This adds a way of doing it quickly for very long lists.

This Pull Request fixes/closes #1295 .

It changes the following:

• adds 4 new key combos (focus_pane_$direction), defaulting to ctrl+arrow
• uses those combos in the status tab to switch views

Right now it doesn't add these combos as commands, since the available commands is already very crowded and confusing, but I can add the commands if necessary.

I followed the checklist:

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

[extrawurst]

Currently, the only way to switch between the tree and stage is by scrolling through the entire list.

that’s not true there is a hot key for that already

[extrawurst]

You can simply rebind that toggle to whatever you prefer

[alexmaco]

that’s not true there is a hot key for that already

Somehow I missed that, I thought it would send the current tree item to stage instead 😆.

[alexmaco]

I think #1295 can probably be closed in that case.