Vertical layout option for portrait monitors

[YaLTeR]

Instead of infinite horizontal and fixed vertical space, for portrait monitors it makes sense to have infinite vertical and fixed horizontal space. So the same scrolling layout, but going down instead of to the right. And I guess workspaces go sideways then?

Originally requested in: #757

Unfortunately, this would be quite an annoying and complex refactor in the code.

As an easier alternative, #401 will let you open windows as maximized by default on the portrait monitor.

[Ornanovitch]

As a dual monitor person with a portrait monitor, I would love to see #401 rather than this solution :)

[chilledfrogs]

Both are useful for mobile devices

[silvigon]

I would really love this! #401 would certainly help, but for my use case this would be the ideal solution.

[isti115]

I think that while it might seem like a big refactor now, it will probably only get harder later, not easier, so it's better to get it done as soon as possible. While I'm not really familiar with the codebase yet (I'm just now looking into the source to decide whether to try to move here, or try to write my own scrolling layout generator for RiverWM), I think that generalizing everything to be defined in terms of a "main" and "sub" axis instead of "X"/"Y", "width"/"height", etc. with "start"/"end" instead of "up"/"down" /"left"/"right" would be the most beneficial in the long term for the project. Then it would be straightforward to switch between horizontal (or "row", since I'm already kind of using flexbox terminology) and vertical (or "column") layouts. (The original meaning of "column", as it currently exists would have to be replaced by something direction-agnostic, like "stack", while "strip" could stay as it is.)