Rewrite ActionGroup from Spinner to Button+DropDown

[KeyWeeUsr]

Compared to the previous behavior the current implementation doesn't cripple the graphics anymore i.e. when you click on a Button in the DropDown, you can actually see the smooth changes of the color e.g. like when you click on_press in a pure Button widget.

Then, using Spinner in the first place makes no sense to me at all because the only thing used from there is the actual DropDown and an overhead + bugs it brought when trying to set is_open in a weird way.

Also, sometimes when opening one group and then another (click on Group 1, then on Group 2), the DropDown could stay opened. And sometimes it disappeared correctly.

Closes #5337, #5338