Add undo/redo commands

[TyJOrtiz]

I was wondering if you could implement undo/redo commands

CodeEditor.Undo();

method:

var result = await this.InvokeScriptAsync(@"function runUndo() { editor.getModel().undo(); }; runUndo();");

CodeEditor.Redo();

method:

var result = await this.InvokeScriptAsync(@"function runRedo() { editor.getModel().redo(); }; runRedo();");