Use layer shell so that in wayland (sway) the popup can appear on top of fullscreen

**Is your feature request related to a problem? Please describe.**

In Sway if I press my keyboard shortcut for `copyq menu` it will appear behind a "fullscreen" window.

**Describe the solution you'd like**
there is a protocol for dealing with these situations, apps can express the need to be on the overlay layer using the layer shell protocol and thus be visible in all situations.

Similar apps like the wayland fork of rofi have options to use the overlay layer.

**Describe alternatives you've considered**
None I could think of.