Provide a command to print the layout tree

[jlargentaye]

For a beginner, the implicitness of containers can make it confusing to understand why windows are being organized in a particular way. For example, I couldn't understand why my editor window wasn't tiling with a terminal window, until I realized I had accidentally made the editor window floating, and even so it wasn't clear where in the layout tree it was.

I wished I had a command that could dump the layout tree, which would have helped me understand what was going on.

[llimllib]

I'm not a contributor to the project, but I'm pretty sure this is the last open todo from #16

I'm just here because I would really like this too, and had searched and found that issue.

(I'm having a lot of fun using aerospace but not being able to see the tree makes it like learning with a blindfold on!)

Also a dupe of #55 I think

[nikitabobko]

Duplicate of #16