Feature request: Add visual cue for container hints vs window hints

[markstos]

Containers in tiling window managers like Sway are a bit confusing because they are invisible.

#146 would help some because it visually offsets adjacent hints so that they at least don't run together.

Still, it could be clearer which hints belong to a container and which belong to a window. I propose this solution:

Hints for containers should have a visible border around the hint

The hint for the current container or window has inverted coloring. It should have an inverted border color.

Since a container might be itself as visualized as a border, this seems like a useful hint.

#75 is example issue report where it it wasn't clear that a container was hinted. Instead it appeared that the window had a four character hint.

With Sway, it appears that containers are found in the get_tree output where window is null and app_id is null or missing. Also, containers have a child nodes array of non-zero length, while application windows have a zero-length nodes array.