DATASET TAB: Implement the Package option in the DatasetButton

[gjwgit]

Description

R packages can provide provide their own datasets. In R we can check each locally installed R package for their datasets (need to check the latest way of doing this in R - seems like ls(sys,frame(0)) and checking the results for is.data.frame() or 'inherits(., sqlite.data.frame) etc is no longer the way to do that (but is still what old Rattle attempts to do).

This task will identify how to find R datasets from amongst the current R packages installed, and the parse that list in rattleng to then make available as a list with the PACKAGE button when choosing a Data Source:

On choosing one of the named dataset packages (like rattle:weather where rattle is the package and weather is the dataset), it is loaded into RattleNG

Why

So that a user can access any one of the very many datasets provided by the different packages in R.

Closing Criteria

• [ ] Click Package to get a list of package datasets to choose from
• [ ] Packge:dataset name populates the data name text field
• [ ] The dataset is loaded via an R script into the template variable ds in the R process

[gjwgit]

Implementation steps on clicking the Package button:

• [ ] Write a new R script assets/r/list_package_dataset.R) to output a list of packages
• [ ] Scrape the list into dart
• [ ] Populate a GUI single selection list
• [ ] Write a new R script assets/r/dataset_load_from_package.R
• [ ] Execute that script with the rattle.path identified