display tooltip when hovering sliders

Submitted by Liv

Assigned to Jannis Pohlmann

Link to original bug (#6637)

Description

It would be helpful if xfce4-mixer displayed a tooltip with a message similar to "Speaker: 56%", while hovering the level-changing sliders or the associated label, or when changing the levels either using a mouse-click or the scroll-wheel.

Currently it doesn't and there's no easy way to find the exact current or new sound level; the panel plug-in displays a tooltip only for the mixer track.

Version: 4.6.1