Configurable (smaller) horizontal spacing between icons

[szpak]

There is (relatively) significant horizontal spacing between presented icons:

Changing icon size doesn't help much. For laptops with lower resolution having 4+ icons can take measurable amount of the top panel. Maybe it would be possible to (on demand) decease that spacing? For me, even an ability to easily change it manually in code would be useful.

[Finii]

Maybe use the extension mentioned in #219 (comment) to generally/consistently reduce the padding.