[Frontend] Convert main left pane elements to flex layout

open #250
Markup mods in browse.html;
Renamed .holder-create-and-search to
.holder-treeview-elements;
TO-DO: fix search results to scroll properly;

platform/commonUI/general/res/sass/mobile/_layout.scss

@@ -42,7 +42,7 @@
         }
     }
 
-    .holder.holder-create-and-search {
+    .holder.holder-treeview-elements {
         right: $bodyMargin !important;
     }