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/core_lib/widgets/uiscrollbar.lua

@@ -0,0 +1,30 @@
+UIScrollBar = extends(UIWidget)
+
+function UIScrollBar.create()
+  local scrollbar = UIScrollBar.internalCreate()
+  scrollbar:setFocusable(false)
+  return scrollbar
+end
+
+function UIScrollBar:onSetup()
+  --self.getChildById('upButton').onClick = function() self.navigateUp() end
+  --self.getChildById('upButton').onClick = function() self.navigateDown() end
+end
+
+function UIScrollBar:attachWidget(widget)
+  self.attachedWidget = widget
+end
+
+function UIScrollBar:onStyleApply(styleName, styleNode)
+  if styleNode['attached-to'] then
+    local id = styleNode['attached-to']
+    local parent = self:getParent()
+    local widget
+    if id == 'parent' then
+      widget = parent
+    elseif parent then
+      widget = parent:getChildById(id)
+    end
+    self:attachWidget(widget)
+  end
+end

modules/core_lib/widgets/uisplitter.lua

@@ -50,9 +50,10 @@ function UISplitter:onMouseRelease(mousePos, mouseButton)
 end
 
 function UISplitter:onStyleApply(styleName, styleNode)
-  if styleNode['relative-margin'] then
-    self.relativeMargin = styleNode['relative-margin']
-  end
+  --TODO: relative margins
+  --if styleNode['relative-margin'] then
+  ---  self.relativeMargin = styleNode['relative-margin']
+  --end
 end
 
 function UISplitter:canUpdateMargin(newMargin)