moving the Rshiny to the package (see SSDM example)

[dmcglinn]

Hey @FelixMay and @KatharinaGerstner

I recently saw this R package which was published in MEE: https://github.com/sylvainschmitt/SSDM

The thing I found interesting with regard to mobsim and mobsim_app is that they created a function called gui() which called the shiny app when the SSDM package is loaded. I thought this was a pretty cool implementation and something to think about if you guys decide to develop and update the shiny app further.