Review Request: Change device notifier tooltips to respect plasma tooltip style

[Jacopo De Simoi]

> > Like one more font face
> > and not aligned with anything either.
> 
> the font should be the same as the top header, so there shouldn't be another 
> font face. as for alignment, iirc they are right aligned.

You recall correctly, but it has been changed since :)
Right aligning with (un)mount buttons always visible gives a weird feeling, as if the buttons were part of 
a column which name is given by the category name. 
The current visualization (i.e. left aligned category name below a separator) recalls the usual category view in other parts of the workspace (e.g. system settings), although admittedly it could be made a dedicated widget in 4.6.

The category title should be aligned with either the device icon or the itemBackground; the former looks decent with no hovered item, the latter looks better in the other case. In any way, since most icons are not square, the category title is pretty much /never/ aligned with the icon (it tries to do so now), so I'll just go and left align it with the itemBackground.