Show ShinyApps deployment dialog in preview window for Shiny docs/apps

This change makes it possible to initiate a deployment to ShinyApps directly from the preview windows for Shiny docs and Shiny apps. 

The change works as follows:
- The ShinyApps singleton (which knows how to show the dialog and fire corresponding events) is now initialized in these specific satellite windows 
- The main frame is now passed (via JS callbacks) the output of the deployment dialog (chosen account, app name, etc.), which it uses to fire the same deployment initiation event fired by the dialog when it's running in the main frame.