RStudio addin

[dkilfoyle]

Loading library in RStudio will register as addin with basic wrapper UI to select dataframe.

[smartinsightsfromdata]

@dkilfoyle Apologies for taking so long. I would have accepted your PR but now there are conflicts in the code.

Would you be so kind to review?
Many thanks for your patience.

[smartinsightsfromdata]

@dkilfoyle I belatedly tried to merge, but there are quite a few problems with R CMD check that in the end prevent me to merge: I wouldn't be able to pass the R cran checks.

My apologies.

I would recommend to try R CMD check or the rstudio check tools (as cran)

Moreover I wasn't able to use it with anything but iris (but this is maybe my fault! I do not know much about rstudio addins). How do you use it with other dfs?