[wf-panel] is not sticky on cube

[mbx162]

Describe the bug

the wl-panel is sticked on the cube-surface, not on the screen. This makes the panel appear multiple times on all cube surfaces and flicker every time the cube is rotated (cube.rotate_left / rotate_right). The flicker is most noticeable if the animation_time is 100

To Reproduce Steps to reproduce the behavior:

1. Enable plugin cube (use a cube.initial_animation time of 1000)
2. Enable and configure wl-panel
3. configure cube.rotate_left KEY_LEFT
4. -- see wl-panel on the top/bottom of the screen
5. press KEY_LEFT

Expected behavior The wl-panel is sticky on the screen, not rotated with the cube

Wayfire version 0.7.2, gentoo