Feature Request: implement list-windows --layout

[Petemir]

Hello,

Extracted from a comment on #272:

Would it be/is it possible to filter windows by their layout? Particularly, I am interested in being able to list floating windows... in that case, it would be trivial (as a user) to implement the requested feature

(i.e., a scratchpad).

By the way, many thanks for the app. It's a great tool for those used to i3 on Linux, and it's a comfort being able to keep a similar workflow when changing environment so drastically.

Please let me know if there's anything else I should add. Thanks once again!

[nikitabobko]

The concrete proposal shall anybody decide to submit a PR:

list-windows --layout (accordion|tiles|horizontal|vertical|h_accordion|v_accordion|h_tiles|v_tiles|tiling|floating)

The options are essentially the same as in layout command