New DesktopWindow button, fix to ponder_index

Adds a new button visible in the context menu, which directly opens the Ponder index (using ponder_index)

Also fixes the ponder_index concommand so that it will open an existing panel instead of creating a new one

lua/ponder/command_cl.lua

@@ -18,7 +18,11 @@ end, function(cmd, _, args)
 end, "Open the Ponder storyboard for the given UUID")
 
 concommand.Add("ponder_index", function(_, _, _)
-    Ponder.OpenIndex()
+    if IsValid(Ponder.UIWindow) then
+        Ponder.UIWindow:PonderShow()
+    else
+        Ponder.OpenIndex()
+    end
 end, nil, "Open the Ponder index")
 
 concommand.Add("ponder_restore", function(_, _, _)

lua/ponder/core/userinterface.lua

@@ -14,4 +14,15 @@ hook.Add("PopulateMenuBar", "Ponder.PopulateMenuBar.InsertMenuOption", function(
             Ponder.OpenIndex()
         end
     end
-end)
+end)
+
+list.Set("DesktopWindows", "Ponder", {
+    title	= "Ponder",
+    icon	= "materials/ponder/ui/icon64/magnifier.png",
+    width	= 520,
+    height	= 700,
+    init	= function(_, window)
+        window:Remove()
+        RunConsoleCommand("ponder_index")
+    end
+})