[Mobile] Sanding of mobile styles continues, in progress

open #74
CSS and markup changes for split pane holders;
drop shadow added to tree area;
Tree item cleanups;
This or earlier commit broke treeview nav action;
TO-DO: fix treeview nav action to hide menu;

platform/commonUI/general/res/sass/_mixins.scss

@@ -328,7 +328,7 @@
 }
 
 @mixin verticalCenterBlock($holderH, $itemH) {
-    top: floor(($holderH - $itemH) / 2) !important;
+    top: floor(($holderH - $itemH) / 2);
     bottom: auto;
     height: $itemH;
 }