Support for actions as icons, including support for action visibility

[HadrienGardeur]

With this task, we'll cover the most basic support for actions when displayed as icons:

• displaying an icon
• label when hovering over the icon
• visibility for icons (always visible, partially visible)

[JayPanoz]

Question: we already have an hover set for the top and bottom bars so how does this behaviour should evolve with the requirement of hovering over the icon?

Answer: implementation is good as-is, with top and bottom bars sync’d and actions as part of it.