Rename shinyApp.R to enable automatic shiny detection

[thatsIch]

Shiny requires a specific naming to be auto-detected. Either

• client.R and server.R or
• app.R

though that is not required since given through the documentation:

• A directory containing server.R, plus, either ui.R or a www directory that contains the file index.html.
• A directory containing app.R.
• An .R file containing a Shiny application, ending with an expression that produces a Shiny app object.
• A list with ui and server components.
• A Shiny app object created by shinyApp.

it is better to do by the conventions.