power: Implement new power menu design

This is a part of the new system status design, see
https://wiki.gnome.org/GnomeShell/Design/Guidelines/SystemStatus/
for design details.

https://bugzilla.gnome.org/show_bug.cgi?id=704368

data/theme/gnome-shell.css

@@ -225,10 +225,6 @@ StScrollBar StButton#vhandle:active {
     font-weight: bold;
 }
 
-.popup-device-menu-item {
-    spacing: .5em;
-}
-
 .popup-status-menu-item {
     font-weight: normal;
     color: #999;
@@ -247,10 +243,6 @@ StScrollBar StButton#vhandle:active {
     icon-size: 1.09em;
 }
 
-.popup-battery-percentage {
-    padding-left: 24px;
-}
-
 /* Switches */
 .toggle-switch {
     width: 65px;