Make visible titles from the control bar on hover

[davidbgk]

This is an attempt at making labels of buttons from the control bar more explicit when hovering (it reuses the title attribute of these links).

[yohanboniface]

It's a bit broken when the button has a border-radius. Should we style the right border of the title element to make it like an arrow or something ?

[davidbgk]

For the border radius, we can fake the junction with a few less px of the negative margin, for the arrow though it will get harder because we are already dealing with an extra element from ::before and no extra markup.

Anyway, that was more a proof of concept to verify it it's useful or not to go down that way.

Also, there will probably be some issues with translations lengths for some verbose languages.