We're currently using the "enter fullscreen" and "exit fullscreen" icons in the upper right corner of every app panel to make the header disappear and appear again.

I'd like to free up these icons for actual fullscreen views, which are likely going to appear soon for any app. We've thus developed an actual icon to hide and show the header from any app panel.

Please thus replace the current "open-fullscreen" with "collapse-header" icon and "close-fullscreen" with "expand-header" icon generically for every app.