panels: Restyle only the home bar on state changes
So far we added the style class to the whole panles which means recalculating the style for all widgets (including the app grid). This way we need to calculate way less new CSS.
Would be interesting if that makes a noticeable difference on the original PP.
Helps: #1177 (closed) Signed-off-by: Guido Günther agx@sigxcpu.org