Make "useful window widths" and "useful window heights" user-configurable through PaperWM extension settings

[jtaala]

Resolves #316, resolves #402

This PR makes the "useful window widths" and "useful window heights" user-settable through the extension pref settings ui.

Inputs supported are percentage or pixel values, e.g. 38.195%; 50%; 61.804% or 400px; 800px; 900px. Mixed input types (e.g. input with % AND px in it) are not supported and will cause the input box to turn red (error css class), as will any invalid input:

Changes are applied immediately (no need to logout/login etc.).

Reset buttons are also provided which will reset width/height values back to the default PaperWM cycle values.

Feedback welcome!

[jtaala]

@ccope could you review / test this one when you get a chance?

[jtaala]

@Gelbana @tadfisher @smichel17 - just FYI, asked ccope to review this one (since he requested it in #402).

Thoughts or any improvements suggestions super welcome!

[smichel17]

On reflection, I use "useful window widths" a ton but I don't think I've ever actually used "useful window heights" (and in fact, I didn't realize it was a thing until just now). Is it something you added because you wanted to change it, or because you were also making the window widths configurable and it felt like the heights should be, too?

[jtaala]

On reflection, I use "useful window widths" a ton but I don't think I've ever actually used "useful window heights" (and in fact, I didn't realize it was a thing until just now). Is it something you added because you wanted to change it, or because you were also making the window widths configurable and it felt like the heights should be, too?

Heights were there, I actually use them quite a bit as I have a layout I like for several applications and being able to set a specific height (that I use) was part of the early intent of this PR. So bit of a mix - they were there (so might as well have a setting for them like widths), plus I wanted to change/use them anyway.

[jtaala]

Yep, I guess I wouldn't mind have the width/height settings hidden / or changing them through dconf, a few thoughts though:

• having them in settings allows changing them without needing a shell-reload (which is handy for fine-tuning without needing restart/login-logout if in wayland)... but there's ways to keep that behaviour with changes via gsettings/dconf;
• it's much easier to let users know when they input invalid inputs if in settings (e.g. input boxes turn red) - users will probably try to input/mix % and px values (or some other invalid inputs) and currently the box turns red letting them know when inputs aren't right. We could throw an error user notification when they try to use the invalid widths/heights though... so maybe this one isn't such a big deal.