Allow collapsing CI builds right sidebar for all window widths

Description

On CI builds, when the window is really thin you can collapse/unfold the right side bar as shown in this screenshot: Capture_du_2016-10-11_16_03_42

I would love to have this possibility whatever the width of the window is:

  • this would add coherence with the other right sidebars (in issues and MR)
  • this would be a big improvement for vertical screens.

Proposal

Keep the collapse button whatever the width of the window is.

Links / references

Replaces #13940 (closed) that was kind of outdated.