Sample notebook for AGOL interaction and Sample Shiny Application

[gbrunner]

This notebook shows how to use the arc.connection to get a token, connect to AGOL, search content, and load content into an interactive map. I think it'd be a good addition to the repo. What do you think?

[gbrunner]

I also added a sample shiny application in https://github.com/gbrunner/R-Bridge-Tutorial-Notebooks/tree/master/shiny. This could make for a nice demo. In the shiny app, I'm using a custom package I wrote for AGOL interaction, https://github.com/gbrunner/arcgis-r-demos. I could probably swap this our for the arcgisbinding package capabilities.