Icon deletion animation could be smoother

[anthony0br]

I propose the other icons should smoothly fill the void space when an Icon is deleted, in a similar way to how they move when an Icon is created or resized.

This video shows the current asymmetric behaviour where when the "Back" button is added (by calling Icon.new) the empty space is maintained with a smooth animation (ignoring the text bug in issue #100). But, the space is filled abruptly when it is removed with :destroy().

https://github.com/1ForeverHD/TopbarPlus/assets/129159900/85f4323b-b6af-4695-9720-ee5fe815c116