Open a twui.xml file, from disk only to start

[chadvandy]

• [x] Route command from MenuBar
• [x] Open up a file dialog
• [x] Filter for only twui.xml
• [x] Class in background to handle the pointer to that file's location, any loaded details, any changes, etc
• [x] Display XML contents in one section
• [ ] Display hierarchy treeview on one side
• [ ] Display properties of selected element in hierarchy on another

File -> Open Twui

Display XML contents in one tab Display the treeview of the TWUI in a side view Display properties of each element, based on treeview selection, in another side view