Create / modify UI Schema (tree based)

[TheZoker]

Use the existing editor and integrate it within visual studio code

• Get the current tree editor running in theia
• Integrate into our theia extension
• Integrate into our vs code extension
• NEW: add feature: generation of Controls in the Tree
• NEW: add feature: linkage between controls and attributes (i.e. when adding control with attribute(s) -> question: "want to add to schema, too?")

TreeView in vscode:
https://github.com/Microsoft/vscode-extension-samples/tree/master/tree-view-sample