Minor Edits to UIMiniWindow

Allow for a double click on the Top Bar of a UIMiniWindow to function
the same as pessing the minimize/maximize button.

modules/client_skins/skins/default/styles/miniwindow.otui

@@ -15,6 +15,17 @@ MiniWindow < UIMiniWindow
   $on:
     image-border-bottom: 2
 
+  UIWidget
+    id: miniwindowTopBar
+    anchors.top: parent.top
+    anchors.right: parent.right
+    anchors.left: parent.left
+    margin-right: 3
+    margin-left: 3
+    margin-top: 3
+    size: 258 18
+    phantom: true
+
   UIButton
     id: closeButton
     anchors.top: parent.top

modules/corelib/ui/uiminiwindow.lua

@@ -82,6 +82,15 @@ function UIMiniWindow:setup()
       end
     end
     
+  self:getChildById('miniwindowTopBar').onDoubleClick =
+    function()
+      if self:isOn() then
+        self:maximize()
+      else
+        self:minimize()
+      end
+    end
+
   local oldParent = self:getParent()
 
   local settings = g_settings.getNode('MiniWindows')