Editor shadow is drawn over menu

[gruehle]

Steps to repro:

1. Open a file and scroll down a bit to get a top scroll shadow in the editor
2. (Optional, but makes the bug easier to see) Make the window narrow enough that the filename is wrapped to a second line
3. Open a menu

Results:
Scroll shadow is on top of the menu.

This was fixed recently, but I think it got broken again when the z-index constants were added.

[gruehle]

Confirmed fixed. Closing.