ui and graphics changes

* implement draw clipping using opengl stencil buffers
* allow to create Widgets by style name with g_ui.createWidgetByStyle
* styles can now have children widgets
* make proper use of the isNotPathable in pathfinding
* add scrollbar skin

modules/client_entergame/characterlist.otui

@@ -18,11 +18,17 @@ MainWindow
   TextList
     id: characterList
     anchors.fill: parent
-    anchors.bottom: next.top
+    anchors.bottom: accountStatusLabel.top
     margin-bottom: 5
     padding: 1
     focusable: false
 
+  VerticalScrollBar
+    attached-to: characterList
+    anchors.top: characterList.top
+    anchors.bottom: characterList.bottom
+    anchors.right: characterList.right
+
   Label
     id: accountStatusLabel
     text: |-