When opening a dialog in the editor, select the "default" event automatically

[cwhitten]

When a dialog is opened in the editor, we should automatically select the default event:

• If an event handler is present for the beginDialog event, select it
• Otherwise, if an event handler is present for the ConversationUpdate event, select it
• Otherwise, do not select an event, but present a message in the main editor area where steps would normally be present that says "Please select the event handler you want to view, or click "+" to create a new one."

[yeze322]

Events are already lifted to Shell layer, we can close this issue now.