Dynamic window opening direction

[jtaala]

Fixes #727.

This PR adds the ability to change the "direction" that new windows will be opened (e.g. to the right/left of the current window).

It also adds:

• an icon on the Gnome topbar indicating the current mode;
• setting to hide this icon;
• setting to set the modes available for cycling through (e.g. right, left, start, end);
• a keybind to cycle these modes (Shift+Super+w);

Screencast.from.2024-04-19.08-06-43.webm

[jtaala]

P.S. @valpackett, I've changed the icon for the edge mode since the original one reminded me of fullscreen mode.

Having said that, if you have strong feelings towards the original icon let me know (and not the new one) let me know!

P.S.S. have a look at https://flathub.org/apps/org.gnome.design.IconLibrary and let me know if any other ones from there look okay/better.

[valpackett]

P.S. @valpackett, I've changed the icon for the edge mode since the original one reminded me of fullscreen mode.

The new one looks generally better, the edges it shows are rather thin I guess but that's fine