Renamed "varRef" to "reference" in .pzs files.
Add controls for displaying the name and source of a node in NodePropertiesDialog.

Can't edit them yet...
Added NodeItem buttons to open/delete a node.

Opening a ScriptNode opens another tab in the editor.
Opening a LuaNode is not implemented yet.
Added undo/redo buttons to the toolbar.
Allow editing the name of a node, deleting/reordering connections.

NodePropertiesDialog gained undo/redo buttons.
Node variable name/value fields are as wide as needed.
New ScriptSceneDialog allows adding/renaming/reordering/removing inputs.

Now for the outputs...
Allow editing outputs in SceneScriptDialog.
Merge all MoveNode changes on the same node into a single undo command.
Fixed ProjectTreeModel::toItem().
Clicking on a node variable value pops up a dialog to edit the value.
Update QAction enabled state when stuff happens.
Set global _SCRIPTED_ when parsing .lua files.

Since a .lua file may have a bunch of crud we can't execute, the .lua file
can put the 'editor' table at the top of the file, then do:

    if _SCRIPTED_ then return end

after the table to avoid stuff the editor can't handle.
Allow drag-and-drop from a node variable onto another node variable.

This is in anticipation of implementing Event nodes.
Removed erroneous .autosave file.