[Gtk-3.20] Re-adjust titlebar(for Unity), headerbar and toolbar height

Now that our buttons are much smaller we can re-adjust titlebar, headerbar and toolbar height.

gtk-3.20/scss/apps/_unity.scss

@@ -6,7 +6,7 @@
 
 @include exports("unity") {
     UnityDecoration {
-        -UnityDecoration-extents: 28px 1px 1px 1px;
+        -UnityDecoration-extents: 24px 1px 1px 1px;
         -UnityDecoration-input-extents: 10px;
 
         -UnityDecoration-shadow-offset-x: 1px;

gtk-3.20/scss/widgets/_toolbar.scss

@@ -9,7 +9,7 @@
     @include linear-gradient($bg);
     @include border($bg);
 
-    padding: $spacing;
+    padding: $spacing * 2;
     color: $fg;
 
     &:disabled {